Effect of Si addition on the microstructure and mechanical properties of ECAPed Mg-15Al alloy

In the paper, Si element was added in Mg-15Al alloy and processed by the equal channel angular processing (ECAP) for 4 passes using route Bc at 300 °C. Microstructure characteristics of experimental alloys before and after ECAP were observed by OM, SEM, EDS and XRD. Tensile test (25, 150 and 200 °C) was carried out by a WDW-100KN tensile testing machine. The results show that the grain size of as-cast Mg-15Al alloy was decreased with addition of 1 wt% Si element, and new Mg2Si phase formed in the matrix. Meanwhile, network β-Mg17Al12 phases tend to form with the increasing amount of β. After processing by ECAP, the net structure of β-Mg17Al12 phases was disappeared and the morphology was modified. Moreover, the grain size of α-Mg matrix was decreased sharply, from 11.3 μm (in Mg-15Al) to 5.98 μm (in Mg-15Al-1Si), and Coarse Chinese script Mg2Si phase emerged in Mg-15Al-1Si alloy was broken into particle with dimension of ~3 μm by ECAP simultaneously. As a result, the mechanical properties of Mg-15Al-1Si and Mg-15Al alloy were improved by ECAP and the increased amount of Mg-15Al-1Si alloy was greater than that of Mg-15Al, about 51.6 MPa in room temperature tensile strength. The Mg2Si phases with high melting were fragmented by ECAP and distributed uniformly in matrix, thus, the mechanical properties of ECAPed Mg-15Al-1Si alloy were more excellent at high temperature, comparing with other experimental alloys.