The Effect of Processing Pass on the Microstructure and Mechanical Properties of a Friction Stir Processed As-Cast Mg-6 wt % Sn Alloy

Abstract

In this study, as-cast Mg-6 wt % Sn alloy is subjected to one-pass and two-pass friction stir processing (FSP). The effect of processing pass on microstructure and mechanical properties of FSP Mg-6Sn alloy is investigated. It is found that one-pass FSP leads to the breakage and partial dissolution of the Mg2Sn phase in the stir zone (SZ) and two-pass FSP leads to the further dissolution and dynamic precipitation of the Mg2Sn phase. Dynamic recrystallization (DRX) takes place in the SZ of an Mg-6Sn alloy undergoing FSP. Compared to one-pass FSP, two-pass FSP brings about further grain refinement in the SZ. A strong {0001} basal texture is developed in the SZ of a Mg-6Sn alloy from FSP and the change of the sample region or processing pass has little influence on the texture. Compared to an as-cast Mg-6Sn sample, one-pass FSP brings about significant improvement in mechanical properties. Two-pass FSP leads to the further increase in yield strength (YS) and ultimate tensile strength (UTS) but elongation (EL) is reduced. The continuous increase in strength is attributed to the grain refinement and the dissolution and dynamic precipitation of Mg2Sn phase achieved by FSP.

Evaluating the microstructure and mechanical properties of friction stir processed Al–Si alloy

“…Although, the average size of intermetallic compounds decreased with increasing the number of passes, according to Figure 6(d,e), the copper-rich particles size increased after third pass (this average particle size in as-cast base metal and first to the fourth pass is 2.11, 0.51, 0.50, 0.33, and 0.46 µm, respectively). Owing to plastic deformation during FSP, high-density dislocation and vacancies were formed in the stir zone with increasing FSP passes, and also a high diffusion path was created [23, 24] that resulted in diffusion capability enhancement of copper and coarser copper-rich particles. CuAl 2 is extremely brittle, hard, and lacking in ductility at ambient temperatures [25].…”