Modification and refinement mechanism of Mg_2Si phase in Sr-containing AZ61-0.7Si magnesium alloy

The effect of Sr on modification and refinement of the Mg 2 Si phase in an AZ61-0.7Si magnesium alloy has been investigated and analyzed.The results indicate that Sr can effectively modify and refine the Chinese-script shaped Mg2Si phase in the AZ61-0.7Si alloy.By adding 0.06wt.%-0.12wt.%Sr to AZ61-0.7Si alloy,the Mg2Si phase in the alloy can be changed from the initial coarse Chinese-script shape to fine granule and/or irregular polygonal shapes.Accordingly,the Sr-containing AZ61-0.7Si alloy exhibits higher tensile and creep properties than the AZ61-0.7Si alloy without Sr modification.The mechanism on modification and refinement of the Mg2Si phase in Sr-containing AZ61-0.7Si alloy is possibly related to the following two aspects:(1)adding Sr may form the Al4Sr phase which can serve as the heterogeneous nucleus for the Mg2Si particles and/or(2)adding Sr may lower the onset crystallizing temperature and increase the undercooling level.

Comparison of Sb and Sr on modification and refinement of Mg_2Si phase in AZ61-0.7Si magnesium alloy

The effects of Sb and Sr on the modification and refinement of Mg2Si phase in an AZ61-0.7Si magnesium alloy were investigated and compared. The results indicate that the difference of Sb and Sr in the modification and refinement of Mg2Si phase is significant. Addition of 0.4%Sb(mass fraction) to AZ61-0.7Si alloy can refine but not modify Mg2Si phase. Oppositely,by addition of 0.12%Sr to AZ61-0.7Si alloy,the Mg2Si phase changes from initial coarse Chinese script shape to fine granule and/or irregular polygonal shape. Accordingly,the Sr-modified AZ61-0.7Si alloy exhibits higher tensile and creep properties than the Sb-modified one. The difference of Sb and Sr in the modification and refinement of Mg2Si phase is possibly related to the following two aspects:1) the disregistry at(100)Al4Sr//(100)Mg2Si is lower than that at(0001)Mg3Sb2//(111)Mg2Si(0.69% vs 1.72%) and 2) the onset crystallizing temperature of the Sr-modified AZ61-0.7Si alloy is lower than that of the Sb-modified one(603.1 ℃ vs 606.9 ℃).

Effect of Sb on microstructure of semi-solid isothermal heat-treated AZ61-0.7Si magnesium alloy

The microstructure of semi-solid isothermal heat-treated AZ61-0.7Si magnesium alloy was investigated, and compared with that of the Sb-modified AZ61-0.7Si alloy. The results indicate that it is possible to produce the AZ61-0.7Si alloy with a non-dendritic microstructure by semi-solid isothermal heat treatment, and adding 0.4% Sb can accelerate the non-dendritic microstructural evolution of the alloy. After being treated at 580 ℃ for 120 min, the Sb-modified AZ61-0.7Si alloys can obtain a non-dendritic microstructure with a higher liquid content (16%-18%) and finer unmelted primary solid particles (43-53 μm) compared with the alloy without Sb modification. In addition, after being treated at 580 ℃ for 120 min, the Mg2Si phases in the AZ61-0.7Si alloys with and without Sb modification change from initial Chinese script shape to granule and/or polygon shapes.

Sr和Sb变质AZ61-0．7Si合金的铸态组织和力学性能

Mg2Si相的变质和细化被认为是改善含Si镁合金力学性能的关键因素之一。研究了Sr和Sb变质AZ61-0.7Si镁合金的铸态组织和力学性能。研究结果表明:添加0.4%(质量分数)Sb对AZ61-0.7Si镁合金中的汉字状Mg2Si相有一定细化作用,但没有明显变质效果。相反,添加微量Sr对AZ61-0.7Si合金中的汉字状Mg2Si相有明显变质和细化作用。在AZ61-0.7Si合金中添加0.03%～0.09%Sr(质量分数)后,合金中的Mg2Si相从粗大汉字状形貌变为细小的颗粒状和/或多边形状。相应地,合金的抗拉性能和蠕变性能得到显著提高。

Ca含量对AZ61-1Si合金显微组织及力学性能的影响

利用OM、XRD、SEM、EDS等方法,研究了Ca含量对AZ61-1Si合金显微组织和力学性能的影响。结果表明,Ca能显著改变Mg2Si相的形态及大小,细化晶界,而对基体晶粒尺寸影响不大。添加Ca后,AZ61-1Si镁合金的力学性能得到明显提高。