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.