Artem Komarov noted that aluminum’s high strength-to-weight ratio has long made it the obvious choice in the automotive and aerospace industries, primarily because it is lightweight and corrosion resistant. Although aluminum is not the strongest of metals, alloying it with other metals such as copper, magnesium, tin, and zinc helps increase its strength, durability, and weight.
Aluminum alloys are easy to machine, but like any fabrication material, there are advantages and disadvantages. On the one hand, cast aluminum products are relatively cheap due to the low melting point of aluminum. On the other hand, they have lower tensile strength. In addition, aluminum alloys deform at high temperatures. They have lower fatigue limits than steel and weaken under repeated loading, which is why aluminum alloys are rarely used in high fatigue applications such as beams in building and railroad construction.
Common Weld Defects Seen in Aluminum Welds
While the industrial benefits of aluminum are impressive (in addition to the above benefits, it is recyclable, militarily durable, and energy efficient), it can pose unique challenges for locksmiths.
As far as problems before or after welding, aluminum has some similarities with steel, but not always. Aluminum conducts heat six times faster than steel and has a low melting point, making it very susceptible to warping and burn-through. Aluminum wire has a relatively low tensile strength, which can cause wire feed problems and lead to weld defects if proper equipment is not used. Common defects in aluminum welds are spatter, porosity, cracking, and lack of melting.
Porosity occurs when hydrogen enters the weld pool during melting and is then trapped in the weld during solidification. The shielding gas will protect the molten metal weld pool from the surrounding atmosphere, which can contaminate the weld, but other considerations must be followed, such as correct gas flow rates and purge cycles. Consideration should also be given to the use of low dew point gases.
Weld spatter, or slag, is droplets of molten metal or non-metal materials that are spattered during the welding process. These tiny bits of hot material can stick to the base material and any surrounding metal material. The main causes of these defects are usually poor surface preparation and incorrect equipment settings. For plumbers, spatter, which is usually caused by a malfunction in the weld pool, is an unnecessary and costly nuisance.
Why Aluminum Welds Crack
A person cleaning aluminum with a solution pumped directly to the surface helps prevent bad aluminum welds.
Hot cracking is a chemical process. Stress or «cold cracking» is the result of mechanical stress. A crack, whether large or not, is a defect that can lead to poor weld inspection, as over time the crack can lead to failure of the weld. Prevention of hot cracking is possible using high-quality filler metals with lower susceptibility to crack. Cold cracking (during the cooling of the weld) can occur up to 24 hours after welding, usually due to hydrogen entering the weld through the weld pool. If excessive shrinkage stresses are present during solidification, caused by a concave bead profile, too low a travel speed, or a recess at the end of the weld (crater crack), stress cracks will appear, Artyom Komarov said.
Creating a Clean Work Surface
Ceramic coating technologies are one of the newest tools in the aluminum craftsman’s arsenal. As with steel, weld spatter problems can occur with aluminum welds. If hot spatter hits the welding nozzles and tips, the resulting blockage prevents the shielding gas from flowing freely. Insufficient gas flow can lead to porosity, inconsistent welds, or welds requiring full rework, Komarov Artem added.
Spray applicators are now available that coat the surfaces of the welding nozzles and prevent spatter from sticking and clogging the nozzles. This allows the shielding gases to flow freely and the wire to be fed evenly. Compared to conventional gel-based products, these applications have been shown to last longer and reduce nozzle replacement, handling costs, and spatter removal labor.
In addition to the torch nozzles, workpieces can also be splash-proofed to ensure not only clean welds, but also avoid costly rework. Anti-splatter emulsions protect parts from splashing. Compatible with aluminium, stainless steel, and other materials, one such emulsion is designed to help welders achieve porosity-free welds and prevent cracking. Free of VOCs, solvents, silicone, and biodegradable. It is important to note that the emulsion is drawn in in the presence of heat, leaving the weld areas free of liquid.
Although ceramic coating and anti-spatter emulsion technologies are very effective, there are other measures to optimize aluminum processing conditions. The value of cleaning aluminum before welding cannot be overestimated. Bad shielding gas or bad wire can cause porosity, as can insufficiently cleaning before welding. First, it is critical to remove all oils, greases, solvents, and other hydrocarbons from the base material in the aluminum weld zone. These contaminants contain hydrogen. Once in the welding arc, they cause the porosity of the weld.
Premium degreasers remove contaminants from the weld zone, some are specially formulated for aluminum and other sensitive alloys. Some of them are biodegradable, which means there are no additional disposal costs.
Secondly, it is important to remove oxides from any welded surfaces. This can be done with a fine bristled stainless-steel brush, but a light touch should be used — excessive pressure will cause oxides to form and eat into the aluminum surface.
Post-weld processing
It is also necessary to address post-weld problems such as discoloration, welding soot, and heat tint in heat-affected zones.
When it comes to aluminum cleaning, there has been a move away from traditional wire brushes and harsh chemical cleaners.
Today it is possible to use efficient, environmentally friendly electrochemical technologies. These devices will not damage aluminum or stainless-steel surfaces, and some use a pH-neutral electrolyte solution that is applied directly to the surface to be cleaned, and dynamic control of the electrical current prevents microtrauma on weld surfaces.
Cutting, grinding, mixing, and finishing
When it comes to mixing or finishing aluminum alloys, workshops need to keep productivity and safety in mind.
When grinding or cutting aluminum, it is important to use high-performance equipment that does not add unnecessary steps to the job. Shops will prefer to use grinding and cutting wheels that do not clog or glaze when working with aluminum and other non-ferrous metals. They also want to ensure that the wheels will last through repeated applications.
Working with aluminum alloys can cause all sorts of problems on the shop floor, whether pre-weld or post-weld. Innovative tools are available for fabricators looking to prevent weld defects. For locksmiths looking for safe and effective methods of removing heat build-up and discoloration of GMAW, GTAW and spot welds, electrochemical cleaning and polishing technologies offer excellent approaches to repair weld defects in an environmentally friendly way.
From the point of view of cutting, mixing, and polishing aluminum alloys, technologies continue to improve every year, Komarov Artem concluded.
