aluminum alloys

Weight. Aluminum is three times lighter than steel and yet aluminum can provide higher strength when alloyed with specific elements.

None Magnetic. Since aluminum is nonmagnetic, arc blow is not a problem during aluminum welding.

Thermal Conductivity. With a thermal conductivity rate that is five to six times higher than steel and the aluminum welds watch out for lack of weld fusion especially at the weld starts. With alum being more sluggish and less fluid, aluminum can be welded in all positions with spray and pulsed with relative ease. In contrast to steel the high conductivity of aluminum acts as a heat sink making weld fusion and weld penetration more difficult to achieve on parts > 4 mm.. However on thin parts, the rapid build up of heat in the alum parts can add to high weld fluidity and weld burn through potential.

Aluminum Porosity and Hydrogen. When MIG or TIG welding aluminum, the weld decision maker should always be aware that this is one of the metals most susceptible to porosity. Hydrogen dissolved in the liquid weld metal will try to escape as the aluminum solidifies and the trapped hydrogen will result in weld porosity which is often extensive. The main cause of porosity in aluminum welds is the absorption of hydrogen in the weld pool which forms gas pores in the solidifying weld metal. The most common sources of hydrogen are hydrocarbons and moisture from contaminants on the aluminum base metal and on the filler wire surface. Also water vapor from the MIG or TIG shielding gas will provide the same results.

Hydrogen cracking is common with carbon steels but hydrogen cracking will not occur with aluminum. Hot cracking or solidification cracking is a primary cause for alumin

ALUMINUM Liquation Cracking. In contrast to hot cracking which occurs in the weld, while MIG or TIG welding aluminum liquation cracking will occur in the heat affected zone (HAZ). With liquation cracking low melting point films are formed at the grain boundaries and these films (liquid elements)cannot withstand the contraction stresses during the weld metal solidification. Heat treatable alloys, like the 6xxx and 7xxx series are sensitive to liquation cracking. To reduce the potential for liquation cracking, consider a weld wire with a lower melt temperature than the parent metal. With alloy 6061 - 6082, liquation cracking can occur in the partially melted zone when a weld with good dilution is made with 5356 or similar filler metal is utilized. In contrast when welding the same alloys with 4043 liquation cracking should not occur.



Aluminum Oxides. Aluminum will combine with oxygen to form an aluminum oxide layer. This layer will form instantly as the aluminum surface is ground or machined. The aluminum oxide layer while very thin can also be very porous. The oxide layer will readily trap moisture, oil, grease and other materials adding to the potential for hydrogen pickup. The aluminum oxide layer provides excellent corrosion resistance, however this layer must be removed before welding as it prevents fusion due to its higher melting point (3700 degrees F). The weld arc gas molecules, the fore hand (push) technique, mechanical cleaning, wire brushing, solvents and chemical etching and voltage control are used for the oxide removal. One of the best practices to attain clean alum MIG welds is to use the lowest possible voltage which assures a short arc length, and a concentrated plasma which is beneficial for the oxide removal.