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Welding: Why weld aluminum?
By Ric Havel
As we are all aware, many of the components of the engines our industry remanufactures utilize this "mystery" metal. It first started with manifolds, then cylinder heads, timing covers, oil pans, lower main bearing girdles and finally blocks and all accessory mounting brackets.
Don’t forget the rocker covers, bell housings, transfer cases and transmissions and transaxles. With the never ending pressure for lighter drivetrains, cooling systems, brake, steering and suspension components being the order of the day, aluminum is here to stay and we can count on more being used as fast as the OEMs can melt and pour it.
As new technologies develop for casting, forging and extruding of this very adaptable metal will continue to present many opportunities for all rebuilders, large and small alike.
However, when it comes to welding aluminum there seem to be some misconceptions. The purpose of this article is simply to take some of the mystery out of the perceived difficulties in repairing these components.
Please bear in mind many welding manufacturers and distributors, as well as volumes of published books and manuals, offer to help us on our journey through "dark territory," and it may seem that some of what I am saying may contradict what you may have read or heard (two of my "favorite" terms regarding welding: "I read…" and "I heard…").
But believe me, not many authors have contributed any large volumes of printed info regarding how to properly repair a "windowed block" or better yet, the ups and downs of welding dirty, greasy, warped and cracked aluminum cylinder heads with a side of broken guides, bent valves along with chowed camshaft journals. This is not to suggest that my way is the only way to have success, but I hope to open up the avenues of communication.
Aluminum is a thief of heat and if you think you can use the same welding practices as for steel, stainless steel or chrome moly you are going to be quite surprised.
To survive in the current economic climate, our industry must constantly look for opportunities to become more profitable and still maintain control of our profits. We must always look for ways to keep more of what we do in-house and to keep as much of the revenue we generate in the business. Whenever we can control what goes out the door, whether it is product or profits we have better control over the "bottom line."
Our industry has historically been the purveyors of solutions to many problem areas of engine rebuilding, and we have always stepped up to meet these challenges with some very resourceful methods.
Having said that let’s examine why welding aluminum makes sense. The question you have to ask yourself is, "Do I want to enter an industry with pre-planned limitations or limitless opportunities?" Although there are other methods of repairing cracked or damaged aluminum components most have limited uses. Certainly, there is a place for alternative repair methods, but TIG-welding skills, when mastered, will allow boundless repair opportunities. TIG welding techniques and procedures remain the same regardless of type or size of damage, and will carry your reparability far beyond where alternatives reach their limits.
Have you ever successfully pinned a burnt camshaft saddle, repaired a missing corner of a casting, repaired corrosion damage or even repaired a spark plug hole that has been repaired by every insert available only to find a hole that you could put your thumb in, with any other method than welding?
Proper Prep And Cleaning
I cannot overstate the importance of cleaning and its effects on your ability to achieve quality welds on aluminum. Here, in my opinion, are potential impacts of various cleaning methods as they pertain to successfully welding aluminum components.
- Chemical cleaning – Chemical cleaning will not remove all hard scale or chemical-resistant additives, resulting in incomplete internal and external cleaning. All of these items contribute to the difficulty of making a porosity-free weld.
- Glass bead blasting – Components to be blasted must first be washed or baked dry, then blasted, causing possible contamination of the weld area when the glass dust cannot be completely removed from the porosity in the casting. When welding temperatures convert glass dust back to base element carbon, porosity in the weld is a certain result. Also significant residue can be left in water jackets, oil passages, threaded holes, etc.
- Wire brushing – Inefficient, insufficient and potentially dangerous to the operator. The best you can expect is to move contaminants from one place to another.
- Thermal cleaning and airless blasting – My experience shows that this combination process is the most efficient and effective approach when welding of aluminum components must be done. All aluminum can be cleaned with one temperature and one blast time. All parts blasted with the proper media (stainless steel) come out ready to weld. With simple pre-preparation prior to thermal cleaning such as seat and or guide removal in areas needing repair, heads come out ready for crack removal preparation.
Seat Removal Procedures
Of course, there are several methods of removing valve seats, but as with cleaning, each varies in its viability to the active machine shop.
Pulling requires an extensive variety of necessary tooling and has significant potential for cylinder head damage. The process is frequently inefficient because some seat designs do not lend themselves to this removal method.
Cutting with abrasive cut-off wheels or die grinding is very labor intensive, dangerous and messy. Many times the seats are not accessible without causing unnecessary damage to combustion chamber areas.
Cutting with seat cutters is a process that usually involves the use of a seat cutter smaller than the O.D. of the seat to be removed and cutting until the old seat spins out. This is too labor intensive, not cost effective due to expensive tooling and set up time, and once the seat is out you still need to clean the pocket area.
Weld shrinking may be your best solution. What is it and why should you consider weld shrinking? It uses your existing TIG welder, requires no consumables and causes no mess. It produces no abrasives flying around, no counter bore damage, no heat build-up and you can remove the average seat in about 15-30 seconds.
First, grind a tungsten to a very sharp point and point your torch at the seat to be removed. Have your welder set on D/C/E/N (straight polarity), the same setting you would use if you were welding steel, strike an arc with the tungsten pointed toward the mid depth of the seat and slowly add current until the seat starts to melt.
At this point, move the torch halfway around the seat’s outer diameter. You will see the arc remains stable since seat material conducts electricity better than aluminum. You will be able to bring the seat into a molten stage – not dripping, just high red heat and a little melting.
Do not go around more than half the diameter of the seat or when it cools it will take on the shape of a football and be harder to lift out. Just stay half diameter and when the seat cools, as fast as you can, put your torch down and use your hooked pick to lift the seat out of the counterbore.
Because most heads will require the removal of several seats, simply heat all necessary seats at one time then lift them out. This seat removal process can be done prior to cleaning, eliminating the process of cleaning to identify the problem only to remove the seat and clean the counterbore again.
Locating, Preparing Cracks
Pressure testing is the only sure way to locate cracks. Powders and developers often show surface flaws and joints of the casting segments as defects. It can be time consuming to coat and develop the entire head and try to locate cracks/leaks. The procedure isn’t exactly cost effective and will actually contaminate an already clean head.
Pressure testing offers advantages of true crack indication that ignores surface defects. Pressure testing equipment will quickly locate not only the large leak but also the small ones as well, in a single, non-contaminating clean test.
With component removal, cleaning and crack detection out of the way, let’s look at crack preparation methods.
Die grinders can cause messy, constant clog-up, and if a lubricant is used to prevent clog-up it contaminates the area to be welded. It is hard to contain flying chips and is not very precise.
Milling with the head fixtured in a seat and guide machine using an appropriately sized center cutting end mill is a better option because clean chips just fall into a chamber or on the cradle. You have constant control over how much and where you want to remove material. Using this method also allows access to areas otherwise inaccessible by other methods, such as valve guide bores, exhaust port floor repairs and deck surface erosion where very controlled removal is necessary.
Remember, only remove the amount of material needed for access to the weld, because removing more than necessary just makes a small crack into a big crack. This means you’ll have to do more welding than is absolutely necessary, and only adds more material to machine away after welding.
This approach of over-welding is unnecessary, non-productive and actually causes many failures and leaks when the machining is done since the crack area wasn’t sealed by filler rod until you have welded beyond the proper shape – it’s a much harder job for the welder to try to "hang a weld" to air. Regardless of your skill level, you just can’t weld air or dirt. You must maintain proper cross sectional material uniformity so not to cause any area to be weaker or stronger than when you started.
By prepping with an end mill and milling until only a "skin" of aluminum is still remaining, we can follow the crack to its terminating points, allowing a good view, a clean cut and less chance of milling through to the water passages.
Proper prep also allows for a more precise weld because you are better able to utilize the shield gases’ shielding benefit and it is much easier to maintain the proper shapes and flow in the water passages. The unique and complex designs used in many castings we repair must be restored to an "as cast" condition or we can be certain of seeing that job again.
Preheating For Welding
With the crack prepared for welding, the next order of business is preheating, and it’s no casual undertaking. Preheating is best done in an electric oven, which can also be used for straightening.
Preheat temperature for both welding and straightening is 500° F. Depending on the weight and the mass of the heads or components being preheated, and the quality of the oven and its controls, the average soak time is going to be about two hours. Remember, the head temperature must be 500° F, not just the oven temperature, so monitor it closely.
The preheat is so important because it serves many functions, including to eliminate your number one problem with welding aluminum – moisture. If moisture is present at the time an arc is struck you will spend a lot of unnecessary time using the welder to do the preheat rather than the oven.
What you can expect to have happen will be little air bubbles or pockets that keep appearing just as you move the torch away from the weld. Try as you might, those gremlins will be waiting just under the surface of your weld – that is, if you’re lucky and persistent enough to keep trying to get them to flow and close up.
Air pockets or spots that simply don’t want to flow are the reaction of the moisture breaking down to its elements and the gremlins are hydrogen molecules outgassing. If you continue to weld under these conditions, you’ll most assuredly get another chance to do the job again. Moisture contamination is one of the most common reasons for your weld to have porosity leaks.
The second reason for preheating is to minimize the amount of amps you’ll have to use to create a liquid puddle to begin your weld. It also serves to reduce the amount of uneven heat needed to complete the weld when you are transitioning from a very thin metal area that becomes several times thicker all in the same weld zone. Proper preheat also minimizes the chance for any distortion/warping.
While the head is preheating, let’s just take a moment to revisit some reconstruction techniques. So as not to interrupt the flow of coolant, we must maintain a proper cross section in the weld area. Proper preparation of the crack area will negate the probability of unnecessary over-welding and plugging of water passages, important components for proper heat transfer, good elongation properties and proper seat retention.
After a thorough preheat, you will be able to weld on the head for about 15-20 minutes. If more welding is necessary, or if the casting is cooling too rapidly, it should be returned to the oven and allowed to soak again to 500° F. Only then should you complete your weld and set the casting down to rest and cool at room temperature.
Generally speaking any properly preheated aluminum part can be welded with a minimum 250 amp welder – at least that’s the story in principle. While there are many welders that will get the job done, they may not lend themselves to being user-friendly or be up to the day-in/day-out duty cycles this work demands. TIG welders are available in many varieties and sizes, but you will need some basic features to work efficiently.
The minimum you will need is 250 amps, but regardless of machine size you’ll need a water cooler and a water-cooled torch. There are many such torches to choose from, but I have been very satisfied with a standard #20 water-cooled torch. This torch number is a standard part number that will allow you to utilize some of the most popular accessories available today including 1/16˝, 3/32˝ and 1/8˝ collets, collet holders, and several varieties of nozzles and different varying length back caps.
I can utilize this small torch successfully on all aluminum welding due to the help of the preheating. Nearly all of the time I find myself using a 3/32˝ tungsten with a 1-7/8˝ long ceramic nozzle with a 5/16˝ I.D. This small size allows easy access into many tight areas.
The type of welder you will be using also determines the size of the torch. If you are having trouble choosing a welder always err in favor of more amperage rather than making a marginal choice you will regret later.
Many options are available today, but most welders utilize either syncro wave or square wave technologies. Simply put, this is the ability to control the positive and negative current on- and off-cycle times, allowing you better adjustability of maximum cleaning to maximum penetration. This is a feature you don’t want to be without.
Generally, machines 300 amps and larger have a longer duty cycle, which means you can weld for a longer period of time per hour at high amperage without comprising the equipment. I use a 375 amp Lincoln machine, which is a relative newcomer to the field. One of this machine’s features is "auto balance," which makes good use of the square wave adjustments by utilizing the most suitable waveform for a given application. This is not to say I can’t adjust the wave action, it’s just great to let the machine do the adjusting, not me.
Because your amperage requirements will change from moment to moment as you are welding, a foot-operated amperage control is much like the gas pedal in your car – it allows instant changes in amperage.
"Crater fill" is another feature that makes life a little simpler for a welder. This allows for termination of the weld in a very controlled manner, not immediately cutting the current flow, but progressively decreasing it over a matter of seconds predetermined by the welding operator. This enables the operator to complete the weld without forming a crater at the end of the weld.
Additionally, I couldn’t go much further without mentioning the need for high frequency control. This makes starting the arc in A/C mode very easy and also non-contaminating. The high frequency function assists in keeping the arc established during the time the wave action changes from positive to negative, although this may change with the onset of several new machines using inverter technology.
Now comes the choice of tungsten electrodes. In selecting electrodes for TIG welding, five factors must be considered: material, size, tip shape, electrode holder and nozzle. Tungsten electrodes are available in two finishes: clean, which indicates a chemical cleaning to remove impurities from the drawing/swaging operations and also ground, which indicates the surface imperfections are removed by centerless grinding. You should always choose "ground" electrodes.
At the inception of TIG welding in 1941 (then referred to as Heli-Arc) there were only a few tungsten electrodes to choose from. Heli-Arc was developed to address the need to weld aluminum and magnesium for aircraft applications. The shield gas of choice at the time was helium and the electrode was pure tungsten. Pure tungsten electrodes, which are 99.5 percent pure, are the least expensive, but they also have the lowest current-carrying capacity on AC power and provide low resistance to contamination.
So much for the "proper application." Helium was soon replaced by argon gas, since argon is about one-third the cost of pure helium and allows much greater control over arc current (in other words, the heat or energy developed in a helium arc is about 1.7 times that of an argon arc for a given arc current). Helium is great for heavy, thick (1˝ or greater) sections but it has a tendency to cause burn-through on thin sections.
One of the other common electrodes used then, and still in use today, is 2 percent Thoria. This is an electrode that is alloyed with 1-2 percent Thoria: 1 percent Thoria increases the current-carrying capacity many times that of pure tungsten and 2 percent Thoria has even greater strength to carry current without melting and creating what is known as "tungsten inclusion."
Tungsten inclusion happens as the tungsten melts and it becomes deposited in the weld. When this occurs – and it will, whether the tungsten melts or if you touch the tip of the electrode into the liquid puddle during welding – you’ll have to stop and remove that deposit by grinding it away with a carbide burr. Admittedly, this is not an easy task on a very hot part that at high temperature is very gummy anyway. However, failure to remove that deposit will cause problems during the machining stages. When the time comes to machine the counterbore in the welded area, as soon as the seat cutter contacts the tungsten inclusion the seat cutter will lose the battle and then we’ll have to start over again.
There are a few shortcomings when using thoriated tungsten; one is it doesn’t form a good ball when used in A/C mode. Additionally, thorium is a radioactive element; while school is still out regarding the safety issues related to thoria, the European community has not used thoriated electrodes in decades.
The most suitable electrode for all around A/C welding of aluminum is zirconia. Electrodes containing zirconia have properties between those of pure tungsten and thoriated tungsten with regard to arc starting and current-carrying capacity. These electrodes are recommended for A/C welding of aluminum over pure or thoriated tungsten electrodes because they retain a balled end during welding and have a high resistance to contamination.
That covers the menu of the "basic" electrodes, but it’s not the end of your choices. We have been using five other electrodes over the past several years for various aluminum welding applications. Believe me, there are a lot of benefits to trial and error. It should be mentioned that all tungsten electrodes are not only identified by element content but also by a color band surrounding one end of the electrode, which makes identification much simpler.
These are the colors and alloys you should be familiar with:
The last two have just recently become commercially available. Each of the last four electrodes mentioned has its own characteristics regarding how it behaves with different welding machines. Some are more friendly to the newer control devices on the welding machines; some allow use of a smaller-diameter electrode and smaller gas nozzle, allowing access to very confined areas; others deliver a more stable arc at very low amperage and have very good restart abilities; while others react favorably to different shield gas mixes.
One more piece of the puzzle, shield gases are available in both pure (99.99 percent pure) and mixed varieties. Any of the inert gases can be used for TIG welding but only argon and helium are used commercially. Why don’t we use helium as the Heli-Arc process was designed around? Helium, which has an atomic weight of four, is the lightest of the monotonic gases and ranks second in abundance to argon. Welding grade helium is refined to purity better than 99.99 percent. As mentioned earlier, it develops 1.7 times the heat as argon would in the same circumstance.
The density of argon is approximately 1.3 times that of air and 10 times that of helium. For this reason, argon (because it is heavier) will blanket a weld area and be more resistant to cross drafts than helium. Helium, being much lighter than air, tends to rise rapidly and cause turbulence, which brings outside air (which contains moisture) into the arc atmosphere.
Since helium is about three times the cost of argon, and the required flow rate can be two to four times that of argon, helium as a shielding gas can cost as much as nine times that of argon. Also, just to compare: argon’s atomic weight is 40 and helium’s is 4; argon makes up approximately one percent of the earth’s atmosphere, which provides an unlimited source of the gas through liquidation and separation from air.
Although all aluminum can be welded with argon, as you hone your skills you may want to try a mixed gas. I would first recommend a 75 percent argon-25 percent helium mixture, which will allow you to use the specialized controls and tungsten electrodes. The mixed gas will generate a hotter temperature than that of pure argon, so you will either need larger tungstens, collets, holders and nozzles, or a tungsten that can handle the extra heat and make no changes to the size of your accessories for your torch. Unless you are planning to be performing your welding jobs with the part being above the torch, (suspended in the air overhead) you will only be wasting helium and money.
Now that you have some basic information, we are now faced with the choice of filler material. Yes, of course, I’m referring to welding rod, but consider why I call it filler rod. You are not so much welding two pieces of metal but rather replacing material you removed. By not milling into the water passages but rather removing all but the last thin skin, particularly areas in between valve seats, you will be better able to utilize the shield gas and to allow for good cross section repair.
You won’t have the difficulties associated with trying to weld that wide-gap "big crack," but you’ll instead be able to seal the crack with its own parent metal by using your torch as you would a paintbrush. Just strike your arc and move your torch into the area you milled out and begin to simply melt the sharp edges left from milling. As the edges begin to become fluid, fan the torch across to the area prepped and you will find that the puddle will follow the torch across the crack area and flow the area shut without the use of filler material. This type of welding is referred to as autogenous or fusion welding. Done properly, you will save yourself tons of after- welding material removal, and also find the finished weld replicates the original shapes and thickness.
Although there are several alloys of filler material to choose from, for the work we are performing the field narrows quickly. Never use a filler alloy that is heat treatable to weld any aluminum that is not going to be re-heat treated. This would deliver you a repair that is completely annealed. Rather, use an alloy that comes close to the metallurgical content of the alloy you are going to weld, i.e., aluminum, magnesium, copper, silicon, zinc or iron. Simply stated, after trying many different alloy filler materials I have been most satisfied with #4043 in 1/16˝, 3/32˝ and 1/8˝ diameters.
Alloy 4043 has a substantial amount of silicon to allow for good flow and to contribute to the lubricity needed for welding camshaft caps and saddles. It offers good tensile strength and adequate elongation properties critical to a successful job. Since we are all not metallurgists, there’s very seldom the need to search out another alloy when one works this well.
One thing you shouldn’t do is fall for the "I read about that" or "I heard about that" stories, especially regarding 5356 alloy in combustion chambers and on eroded deck surfaces. Although it has more tensile strength, it also has more magnesium than most castings which is where the extra hardness comes from.
But when 5356 is used on areas that exceed 150° F you can create magnesium silicide and then after a while you’ll get to do that job again. Consider this for a moment. When the casting was first poured do you think they filled part of the mold pattern with one alloy and then another area within the same mold with another alloy?
Don’t be fooled into believing that all common automotive aluminum consists of one alloy (the common number being 356 or 356A or 6061 with a T6 heat treatment). That simply is not the case. Many castings utilize 319 alloy and 390 alloy. Many of the aftermarket performance heads are made of better alloy, but certainly not all the grocery getters we see day in and day out. Remember, we are not always just going to be welding heads and blocks but also oil pans, timing covers, transaxles, transmissions, bellhousings, etc. – anything to keep the profits in-house and the business growing.
Aluminum has a tenacious oxide that forms anytime the metal is exposed to atmosphere; in fact, it is forming on all aluminum everywhere as you read this. In order to penetrate this oxide you must use a stainless wire hand brush to scratch off the oxide just before welding, or, if you are steady handed, using a light touch with a die grinder and carbide burr or brush, to skin away the oxide not only in the immediate weld zone but also around its surrounding area.
Otherwise you will find that to melt that oxide will require over 3000° F, twice the temperature aluminum normally melts. Under typical conditions you’ll be faced with melted aluminum and solid oxide so remove it just prior to starting to weld. After you begin to weld, the shield gas will protect the weld zone from any further oxidation providing you do not move the torch too far from the weld zone or remove your filler rod out of the shield gases’ protection.
Speaking about protection, it’s critical to pay attention to personal safety issues. You will need gloves to handle both the hot part from oven to welding area and also a pair of gloves to wear during the welding. The first set I would recommend for the hot handling are made of a woven combination of Kevlar and Nomex called HOT NOT gloves, and the name says it all. You can carry a preheated part around and never feel the heat. They’re safe to at least 500° F.
You’ll also need a pair for welding. These, simply called TIG gloves, are quite common and are typically made of calf skin, doe skin or goat skin. They’re soft enough to give the operator a good feel of the filler rod and allow for easy feeding into the puddle.
Try to get gloves with a gauntlet cuff to keep the radiant heat from your wrists or use pullover sleeves that still allow either glove to fit over. Sleeves of the same HOT NOT material are available and will save you a lot of pain should you mistakenly rest your arm on the preheated part. A good heavy leather apron or cape-n-sleeves will round out the below- the-neck protection.
How about above the neck? We are seeing more and more welding helmets available today than I think we have heads to fit them on. This is an area where you should do your homework before you buy. The most beneficial helmets for operator safety and comfort are no doubt the "auto darkening" versions, but that is only the tip of the iceberg. Some are battery powered, some are powered by the UV rays generated by the welder with battery backup, many come in a fixed shade (normally 10X), and others offer variable shades. This is where I spent a considerable amount of money learning what suited me best.
Choosing a helmet is not a universal decision, meaning there is no perfect solution that will suit everyone who is going to weld. I have found that my shade requirements may change depending on several factors. I may be welding a long time one day. Perhaps a given job has many shadows or my position over the part may require a wider field of vision.
There’s nothing worse than trying to weld while dealing with sweat running on your glasses. Trying to keep them in place and constantly cleaning the specs so we can do another job can be a real headache. One of the most helpful options I have seen to date is the optical lens covers designed for "optically challenged" welders. These trick little jobs came to me from Jackson Products to evaluate and they won’t be getting them back soon because they are great (but of course, testing must continue!). They are called floor spot magnifier plates and are available in 1.0 diopter through 2.50 diopter. They replace the clear lens in a helmet and are available in 2x4˝ and 4x4˝ so they fit all helmets.
My choice of helmets includes an outside-the-helmet shade adjustment so I can adjust while I’m welding. This dream helmet has battery back-up and is powered by the UV coming from the welder. It offers good lower face coverage to prevent fumes and the UV from giving me a tan that I wasn’t planning on.
Welding aluminum is no special art, but is simply another shop operation that, with some patience and basic knowledge, can bring great profits to your shop. At the end of the day, don’t we all aspire to make at least the amount of labor that the sign says we charge? We also know that when we do we are motivated to do better and do more. Any time a shop can exceed its current labor charges day-after-day guarantees its survival in this ever-changing industry.
Anytime you can complete a job in less time than you are being paid for you should explore those opportunities and build upon them. Repairing and welding aluminum is not just a good opportunity, it is a necessary part of the service we perform for our customers. It’s a critical part of being in the business and you can generate great profits by taking advantage of it. We are in the rebuilding business, so make every effort to keep your profits inside your business.
There are many ways to repair aluminum components used in our industry. I believe the effort and time spent to master TIG welding will return great benefits and profits for all shops. Of course, there are many other facets to this topic that I could not cover within the scope of this article. Some of the more in-depth information could address safety gear and health issues, consumables and reasons for certain techniques. One such topic is the extensive Brinell hardness testing and the many related problems that were once related to cleaning and welding.
If it seems as though I missed some of the many details of repairing any particular component such as blocks or the real profit maker – cylinder heads – I didn’t do so deliberately. Rather I wanted to focus on the primary welding issues that seem to be so mysterious and cause so many problems for many shops.
Ric Havel has more than 18 years welding and consulting experience to the automotive and machine shop industries. He has presented to associations and served as a trainer for many manufacturers including Sunnen Products Co. and Lincoln Electric.