The hardenable alloys contain copper (Cu), magnesium and silicon (Mg + Si), or zinc and magnesium (Zn + Mg).

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1 Welding of Aluminium Much of the successful art of aluminium welding is to be found in careful thought and preparation even before welding is started. Through correct preparation, it is easier to avoid the pitfalls that can trap the unwary. Here are a few facts on base metals, welding methods, types of joint and filler metals. Base Metals Aluminium and its alloys can, in general terms, be divided up into three groups: aluminium (pure aluminium) non-heat-treatable alloys heat-treatable alloys. Aluminiums occur in various degrees of purity. The most common commercial grades contain 99.7, 99.5 or 99.0% aluminium. Non-hardenable alloys, i.e. not suitable for heat treatment, contain small amounts of manganese (Mn) or magnesium (Mg). Al-Mn alloys are often made up of between 1.0 and 1.2% Mn, while Al-Mg alloys with up to 5% are quite common. Al-Mg-Mn alloys are also used. The hardenable alloys contain copper (Cu), magnesium and silicon (Mg + Si), or zinc and magnesium (Zn + Mg). Aluminium and most of the non-heat-treatable and heat-treatable alloys possess good weldability. In the case of hardenable alloys with copper and lead additives, there is a risk of hot cracking and therefore they are difficult to weld. Many casting alloys are also suitable for welding except in the case of those which have high content of copper or magnesium which are unsuitable for welding. Safety First! Warning: Protect yourself & others. Fumes & Gases can be hazardous to your health. Arc Rays can injure eyes & burn skin. Electric Shock can kill. Before use, read & understand the manufacturer's instructions, Material Safety Data Sheets (MSDS) & your employer's safety practices. Keep your head out of the fumes. Use enough ventilation; exhaust at the arc, or both, to keep fumes & gases from your breathing zone & the general area. Wear correct eye, ear, & body protection. Do not touch live electrical parts. See American National Standard Z49.1, Safety in Welding, Cutting, & Allied Processes, published by the American Welding Society, 550 N.W. LeJeune Road,

2 Miami, FL 33126; OSHA Safety & Health Standards, available from the U.S. Government Printing Office, Washington, DC Welding Methods Aluminium is an easily welded metal. However, consideration must be given to both the welding method, the type of joint and the filler material. The two dominating welding methods are MIG and TIG welding, but also gas, plasma, and resistance welding are used as well as welding with covered electrodes. Whether to use MIG or TIG welding depends on numerous factors. The TIG method is better for thin light-gauge materials, when there is a need for good surface finish and when welding from one side, that is to say when the root side is not accessible such as when welding pipes, and when repairing castings. TIG welding of aluminium is generally done with alternating current. We are going to concentrate on MIG. The MIG method is used primarily in the case of thicker or heavy-gauge materials when high welding speed is a priority and also for long, continuous welds. Due to the lower heat input, MIG welding results in less distortion in the welding zone. For consistent, reliable feeding of soft aluminium filler wire, the push-pull type of equipment gives the best results. Figure 1. Schematic of the MIG welding process. Note: Pulse-Arc welding with MIG is an interesting technology in the context of aluminium welding and is quickly paining in popularity. One of the main benefits of this method is that it gives better control of the molten pool in the case of thin material, and the arc is more stable and there is less spatter. The risk of welding imperfections is also lower. Here are some tips for successfully welding aluminum:

3 Set the power source for reverse polarity (DCEP). 100% argon shielding gas is generally used for MIG welding aluminum. Use a wire diameter appropriate for your application. Generally, thicker wire works better for thicker applications and vice versa. Use the appropriate wire type. ER4043 and ER5356 are the most common wire types for welding aluminum. However, they have different properties and melts at a different speed, which can affect your desired result. When installing the wire spool, check both the spool tension and the drive-roll tension. The spool tension should be less than what would be set for steel wire. Drive-roll tension should provide an even wire-feed rate. Too much or too little drive-roll tension can cause burnback. When installing the gun, be sure the liner extends from the outlet guide back into the drive roll and as far into the contact tube adapter as possible. If the liner is cut too short, it can cause the wire to tangle, creating what is called a bird nest. Because aluminum forms a hard oxide layer when exposed to air, it is necessary to brush the weld area with a stainless steel wire brush before welding. This will help break up the oxide layer. Remaining oxide will be burned off during the weld process. To ensure good arc starts, the end of the wire should be clipped. This removes any balled end that may have formed during welding. The travel speed for welding aluminum is faster than that for steel due to the high thermal conductivity of aluminum. If travel speed is not increased, excessive melt-through is likely on thin aluminum. Periodic inspection of the MIG gun and contact tip will prevent many of the wirefeeding problems associated with aluminum welding. Finally, store aluminum wire in a plastic bag to protect it from dirt and moisture. Filler Metals When welding aluminium, the choice of filler metal must be determined by the composition of the base metal and the demands which will be made on the end product. Generally speaking, aluminium and non-heat-treatable alloys should be welded with a filler metal of the same type of alloy as the base metal. Alloys which are suitable for hardening should be welded with a filler metal with a high content of silicon (Si) or magnesium (Mg) in order to avoid the risk of hot cracking. If there is need of a good match in colour between the welded joint and the base material after anodic treatment, a suitable filler metal should be used. As in the case of the base metal, care must be taken to keep the filler metal clean. On no account must it be contaminated by oil, grease or dust and therefore it must be kept well protected and stored in warm and dry conditions. Types of Joint

4 The type of joint chosen for aluminium welding depends on the thickness of the material and the type and shape of the workpiece. As a rule, no preparation of the joint is required for thinner materials. An ordinary Tee joint is recommended for one sided TIG welding up to 4mm thickness, and two-sided welding for thicknesses, a 50 V-joint with a 2 to 3mm unbevelled edge is recommended or, alternatively, a 90 double V-joint. Good joint fit-up makes the welding easier, saves shielding gas and filler material and also contributes to a higher quality of welding. If jigs are not used, the weldments should be tack welded in the correct position prior to final welding. Where it is possible, use of a root support or backing is recommended. The backing can be either copper or steel. A special characteristic of aluminium is the higher melting point of oxide that forms on its surface, which is mixed into the molten pool, can cause welding defects. The joint surfaces must therefore be scraped or brushed clean using stainless steel wire brush immediately prior to welding. Aluminium is also sensitive to other impurities such a soil, grease, paint and general contamination, all of which can cause pores in the weld. Cleaning of the joint surfaces, as well as the root and top surfaces bordering on the joint is recommended. Bear in mind that welding causes greater deformation in aluminium than it does in steel. It is therefore essential to give good consideration to the welding sequence, the need of pre-setting to allow for contraction, use of fixtures, and so on. Frequent Questions and Answers: What Machine Do I Need? The first decision is what type of machine is right for the job. Keep in mind that a 115 volt wire feeder welder can handle jobs that range from 22 to 12 gauge and with moderate preheating, you can probably weld as thick as 1/8". Be aware that preheating should be limited to 250 degrees F maximum. Another option is a 230 volt machine which can weld from 22 gauge all the way to 3/16". Proper preheat can take the range to 1/4". If you will need to weld a broader range of aluminum thicknesses, consider investing in the 230v machine. Remember, if you plan on doing regular aluminum fabrication, you will need a heavy duty machine. The 115 volt and 230 volt compact MIG welder models are acceptable for occasional aluminum jobs, but not recommended for heavy duty aluminum use. For daily production welding on heavier aluminum, consider a welder that has greater than 200 amps output. After you have chosen your input voltage, another common question you will be asked when selecting a welder is whether you want a continuous or tapped voltage control model. A continuous voltage control model lets you set an infinite range of voltage within the rating of the machine, allowing more adjustability, fine tuning and precise control. This permits you to more easily adapt the voltage to your application and particular skill level.

5 If you're on a budget, opt for the tapped control unit. This machine has a rotary switch with four or five fixed voltage choices. It will not give you the control of a continuous model, but it can be slightly easier to get up to speed with and costs less to purchase and will be adequate for most applications. What Type of Welds Can be Made? For these types of machines, it is best to make welds in the horizontal and flat positions. In general, fillet welds in lap joints are made more easily than groove welds in butt joints. Fillet welds in tee joints are preferred over corner joints. Keep in mind that home welding by an amateur is not recommended for critical welds where failure could result in serious injury. What Type of Shielding Gas is Required? MIG welding aluminum is different than welding steel when it comes to shielding gas requirements. For aluminum, 100 percent argon is the gas of choice, whereas steel welding calls for a mixed gas or 100 percent CO2 gas. The good news is that no special equipment is needed - your existing regulators (with the exception of CO2 regulators) and gas hoses can be used for both pure blends and mixed gases. What Polarity Setting is Needed? All MIG welding, including on aluminum materials, requires electrode positive polarity, while flux-cored processes typically use electrode negative. If you are switching your wire feed welder between processes, make sure to switch your polarity. This is a common mistake that many beginning welders make. What Aluminum Wire Electrode Alloy Type Should I Buy? You will not obtain good results attempting to weld on aluminum with a steel wire electrode. Instead, our recommendation is that compact MIG welders should be limited to.035" diameter 4043 aluminum alloy filler metal. A 5356 aluminum alloy electrode may commonly be recommended by retailers and distributors, since it is a stiffer wire and can be easier to feed. However, with these types of wire feed welders, there is often not enough amperage to achieve a good weld with Even though 4043 is a softer wire, following the proper steps outlined below will ensure good feedability. Do not use other diameter wires. Specifically, you should avoid 0.030" wire (it is difficult to feed) and 3/64" wire (these compact machines do not typically produce enough current to reliably melt this diameter of wire). How Do I Set-Up My Machine to Weld Aluminum? Now that you know the type of machine you want and its capabilities/limitations, it is important to know how best to set it up. Follow these tips:

6 Purchase an Aluminum Feeding Kit Attention to feeding issues is much more critical when it comes to aluminum welding. It is highly recommended that you purchase an aluminum feeding kit, which includes the following items: Non-metallic liner - designed to minimize the amount of friction on the wire U-shaped drive rolls - to avoid crushing or deforming the soft aluminum wire. These drive rolls do not shave the wire like V-groove drive rolls. Using V- groove drive rolls, the resulting wire shavings can clog the liner and lead to feeding problems. Inlet and outlet guides - designed specifically to avoid wire shaving. Contact tips - as compared to those used for the same diameter of steel wire electrode, contact tips for aluminum have larger diameter holes, since as aluminum heats up, it expands more than steel. Therefore, contact tips for aluminum applications are sized small enough to maintain good electrical contact, but large enough to allow for expansion. Load Wire Into the Machine There is a trick to properly loading aluminum wire into a wire feed welder. While the same technique should be used with steel wire electrodes, it is especially important with aluminum wire loading, to avoid feeding problems during welding. With one hand, hold the wire spool securely so it doesn't unravel. Once you remove the cellophane wrapping, hold the loose end of the wire with the other hand - don't let go until you lock the wire into the drive roll. Inexperienced operators commonly let go of the loose end and the spool starts to unravel. If this happens, it cannot be wound back up and still perform properly - you will have to purchase another spool. Set the Wire Brake Tension The idea is to have just enough tension to keep the wire from unraveling, but not too much tension so that it causes a drag on the wire. To do this, set the wire spool brake tension for a minimum setting. Then, load the spool on and feed it through the drive rolls. With everything stopped, if the spool keeps turning by itself, there is not enough brake tension. Be careful though, since too much brake tension can put excessive force on the wire. And, operators shouldn't be surprised at the end of the spool if they cannot feed the last few turns; usually the wire is too stiff to come off easily. Set the Drive Roll Tension This step is probably the most important in the whole set-up process. The experts from Lincoln recommend holding the nozzle about 1" away from an electrically insulated surface at a slight angle. Then, set the drive roll tension close to minimum. Pull the trigger and watch the behavior - as the wire touches the insulated surface, the drive rolls should slip. Tighten down from that point until the wire stops slipping. Again, a word of caution, as wire that is set too tight will tend to 'birdnest'. This means the wire stops at the gun but the drive rolls are still turning. The result is wire feeds out of the drive rolls and birdnests, or backs up and tangles, anywhere along the drive path - at the guide tubes, in the gun liner, etc.

7 Remember, as you set the drive roll tension in the manner described above, that when the gun trigger is pressed, the wire is electrically hot, so always wear a quality pair of welding gloves. Ensure Good Electrical Connections The work clamp should be securely attached to the welding piece in an area free from paint and contaminants. To clean the piece, use a degreasing solvent to remove any oil and grease. Be sure that the surface is dry before you weld. Also, do not weld with flammable material nearby, such as a container of solvent or paint. As a second step, use a clean, stainless steel wire brush to remove all oxides from the surface of the aluminum. Position Is Important As you are welding, keep the gun cable as straight as possible to minimize feeding restrictions on the soft aluminum wire. A bend in the gun cable can make the wire kink and feed poorly. References: