Investigation of porosity reduction, microstructure and mechanical properties for joining of selective laser melting fabricated aluminium composite via friction stir welding

Friction stir welding of selective laser melting printed AlSi10Mg and AlSi10Mg -2% wt. nAl(2)O(3) parts were conducted. This study investigated the weldability and mechanical properties of the welds by evaluating their chemical composition, porosity, weld microstructure evolution, micro-hardness and tensile strength. The selective laser melting fabricated parts were successfully welded with results comparable to friction stir welding of the wrought AA6061 sheet, without the presence of weld defects and porosity. After friction stir welding, the agglomerated and sintered nAl(2)O(3) particles were fragmented and dispersed in the matrix. Significant grain refinement was achieved in the weld with an average grain size ranging from 2.3 to 3.5 mu m due to the dynamic recrystallisation process developing in friction stir welding. Larger grains were observed with the use of a higher tool rotation speed. The precipitation of Si attributed to a reduction in the hardness as well as yield strength of the as-welded material. The addition of nAl(2)O(3) contributed to finer grains and higher hardness due to Zener pinner effect.