Abstract
0.5 mm thick 6061-T4 Al and T2 Cu were butt-joined by micro friction stir welding (μFSW) at different plunge depths (D1=0.04 mm, D2=0.08 mm, D3=0.12 mm), the temperature distribution was studied by numerical simulation. The results showed that the control of thickness reduction and intermetallic compounds (IMCs) are the keys to obtain a joint with excellent performance. When the plunge depth is 0.04 mm, the peak temperature and residence time are both minimum, the reduction rate of the weld thickness and the proportion of agglomerated IMCs are minimum, which are 4 % and 9 % respectively, the average thickness of IMCs layer is only 112 nm. The tensile strength is the largest (94.1 % of Al base material), the joint fails in the heat-affected zone (HAZ) of Al side due to lowest hardness. Agglomerated IMCs (including Al2Cu and Al4Cu9) are formed in the upper nugget zone (NZ), and IMCs layer (including Al2Cu, AlCu and Al4Cu9) are formed in the lower NZ. As the plunge depth increases, the proportion of agglomerated IMCs and the thickness of IMCs layer increases. So, preferential sites of crack nucleation appear at the agglomerated IMCs. Subsequently, crack growth is exacerbated by the inherent brittleness of AlCu, resulting in ductile fracture in the upper NZ and cleavage fracture in the lower NZ.
Published Version
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