Welding of Aluminium and Aluminium Alloys Part 2: Weldability of Aluminium and Aluminium Alloys

摘要

Aluminium and its alloys are used extensively for a wide variety of industrial applications. Welding is widely used as a method of fabrication for these applications. Certain difficulties are faced in welding aluminium due to some special characteristics of aluminium. The rapid formation of refractory type aluminium oxide on the surface impedes proper bonding in aluminium welds. The high thermal conductivity and high co-efficient of linear expansion on heating lead to distortion in the weldment. Several high strength aluminium alloys are sensitive to cracking in varying degrees when welded. Cracks observed in aluminium alloy weldments are basically hot cracks and are found in the weld and in the HAZ. Cracking in aluminium alloy welds is a complex process and is influenced by a combination of mechanical, thermal and metallurgical factors. The chemical composition of the base metal, filler metal and the resulting weld metal determine the cracking risk of the weldment. Risk of cracking can be minimised to a large extent by proper selection of filler alloy. Selection of filler alloy also plays a very important role in achieving the desired properties in the weldment. Apart from the strength and ductility, other requirements of the weldment, like colour matching after anodising, corrosion resistance, least cracking risk, play a deciding role in choice of filler metal. The high strength age hardened aluminium alloys suffer a softening in the HAZ in the as welded condition, due consideration of which should be given in design calculations.