Crystallography of Mg2Sn precipitates in Mg-Sn-Mn-Si alloy

The microstructures of a Mg-Sn based alloy with trace additions of Mn and Si after various ageing heat-treatments were investigated. The alloy was found to contain mostly Mg2Sn(β) precipitates. The morphology and orientation relationships(OR) of Mg2Sn precipitates were analyzed by using TEM. The Mg2Sn precipitates mainly exhibit three shapes: lath, polygon and plate. Four ORs between Mg2Sn precipitates and Mg(α) matrix are repeatedly detected, and two of them have never been reported before. Most of the lath-shaped β precipitates exhibit two OR. One is (0001)α//(110)β, [110]α//[001]β (OR-1), with the long axis along [110]α//[001]β; and the other is (0001)α//(110)β, [100]α//[31]β (OR-2, a new OR), with the long axis along [100]α//[31]β. The polygonal β exhibits (0001)α//(111)β, [20]α//[10]β (OR-3), with several pairs of facets. The plate-shaped β exhibits (0001)α//(111)β, [20]α deviates by about 9° from [10]β (OR-4, a new OR).