From: Investigation of weld defects in friction-stir welding and fusion welding of aluminium alloys
Difficulties encountered | Type of alloy | Metallurgical aspects promoting the defect | Microstructure | Solutions |
---|---|---|---|---|
Solidification cracking | Higher strength alloys (e.g. 2014, 6061, 7075) | ◦ Solidification temperature range ◦ Grain structure ◦ Primary solidification phase ◦ Quantity of eutectic liquid at the end stage of solidification | ◦ Coarse columnar dendritic structure—higher susceptibility ◦ Fine equiaxed dendritic structure with abundant eutectic liquid—lower susceptibility | ♦ Appropriate dilution ratio ♦ Appropriate control of minor alloying elements ♦ Grain refinement—using agents ♦ Magnetic arc oscillations ♦ Reduce strains—preheating ♦ Improve weld bead shape |
Loss of strength in HAZ | Work hardened materials and heat-treatable alloys | ◦ Increase in heat input/unit length—increases the size of HAZ and retention time above effective recrystallisation temperature | ◦ Deformed grains (due to work hardening) that tend to recrystallise (forming strain free, soft grains)—softens the HAZ | ♦ Reduce heat input—weld process like EBW or GTAW |
Liquation cracking | Higher-strength alloys | ◦ Wide PMZ—high thermal conductivity and wide freezing temp range ◦ Large solidification shrinkage ◦ Large thermal contraction | ◦ Grain boundary (GB) liquid—weakens the PMZ | ♦ Appropriate filler material ♦ Reducing heat input—multipass welding, etc. ♦ Decrease in degree of restraint ♦ Oscillating arc method |