Microstructure of dissimilar joint interface of magnesium alloy and aluminum alloy by friction stir welding

Abstract

Friction stir welding (FSW) shows significant advantages in the joining of aluminum alloys in recent years. In this paper, the feasibility of FSW for magnesium joints and magnesium to aluminum dissimilar joints was studied. Specimens were joined by FSW at the feed rate of 3.33-13.3 mm · s -1 and the tool rotational speed of 25 or 50 s-1. In the case of the butt welded magnesium alloy (AZ31), the average grain size in the stir zone is about 10 μm that is smaller than that of in the parent metal. In the case of the dissimilar weld of magnesium alloy to aluminum alloy, mixing is limited and a more mechanical interlocking joint forms. However, the intermediate layer of about 2μm thickness is observed by TEM. Two kinds of phases are observed in the intermediate layer by the electron diffraction pattern. The electron diffraction suggests that one phase is Al 12Mg17 intermetallic compound, while the other phase can not be defined. The mechanical properties of the dissimilar joint are inferior to those of the parent metals especially in the elongation because of the intermediate layer.