Microstructure and mechanical properties of friction stir welded joints of AC4A cast aluminium alloy

AC4A cast aluminium alloy was friction stir welded, and the microstructure and mechanical properties of the joint and its component parts were examined and analysed. In the weld nugget of the weld, a large number of small silicon particles were homogeneously distributed in a continuous aluminium matrix, and the original casting voids were completely eliminated from the weld nugget, which therefore exhibited much better mechanical properties than the base material. In the thermomechanically affected zone (TMAZ) of the weld, there were short silicon plates and no void flaws, accordingly the weld composed of weld nugget and TMAZ exhibited better mechanical properties than the base material. The global joint fractured in the base material, and thus possessed the same tensile strength as the base material. These results clearly show that friction stir welding is an optimum welding process for cast aluminium alloys.