Relationship of Mg2Si morphology with Mg2Si content and its effect on properties of in-situ Mg2Si/Al-Cu composites

The variations of microstructure and mechanical properties with Mg2Si levels in xMg(2)Si/Al-5Cu (x = 1.5, 3, 5, 10 wt%) composites have been investigated, typically low Mg2Si content for the first time. The XRD results confirm the presence of Mg2Si phase without any impurity phases. The Mg2Si phase is mainly in the form of short sticks from 0 wt% up to 3 wt%, and they distribute uniformly inside or around the Al2Cu phase. Once the content of Mg2Si increased to 5 wt%, Mg2Si exists mainly in the forms of short sticks and with a small number of eutectic Mg2Si like Chinese characters. Finally all eutectic Mg2Si phases become coarse Chinese characters in the 10 wt% Mg2Si/Al-5Cu composites. The 3 wt% Mg2Si/Al-5Cu composites exhibit the optimal mechanical properties, and the ultimate tensile strength (UTS), yield strength and elongation in as-cast state are 330MPa, 205 MPa and 7.0%, respectively. The UTS and yield strength are increased by 26.9% and 28.1% than the corresponding values of the Al-5Cu matrix alloy. (C) 2019 Elsevier B.V. All rights reserved.