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Table 3 Common problems encountered in fusion welding of aluminium alloys, metallurgical aspects and prevention strategies (based on (Kou 2003))

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)

â—¦ Solidification temperature range

â—¦ Grain structure

â—¦ Primary solidification phase

â—¦ 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

â—¦ Large solidification shrinkage

â—¦ 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