高压凝固工艺参量对镁合金凝固组织及性能的影响

The Influence of High Pressure Solidification Process on Solidification Structure and Properties of Magnesium Alloys

采用CS-1B型高压六面顶压机,在2~4 GPa高压及不同加热温度下对铸造Mg-7.52Zn-2.91Y-0.54Zr合金进行高压凝固,利用SEM、OM等分析方法研究了凝固压力及加热温度对高压凝固组织及二次枝晶间距的影响,并测试了高压凝固合金的力学性能及耐蚀性能。结果表明,高压作用下凝固能极大地细化镁合金凝固组织,平均一次臂长度由常规铸造下的165μm,减小到2 GPa下的50μm,4 GPa下的20μm;平均二次枝晶间距由常规铸造下的35μm,减小到2 GPa下的8μm,4 GPa下的5μm;晶间第二相由连续网状分布变为4 GPa下断续分布。试验合金的抗压强度由常规铸造的346 MPa提升至4 GPa凝固的446 MPa。在3.5%Na Cl介质中高压凝固合金具有更小的腐蚀电流密度、更正的腐蚀电位。

Under the action of 2-4 GPa high pressure and different heating temperature, the conventional casting ofMg-7.52Zn-2.91Y-0.54Zr was made with the CS-1B high-pressure cubic-anvil press. The effects of squeezing pressure and heating temperature on high pressure solidification microstructure and secondary dendrite arm spacing were investigated by scanning electronic microscopy （SEM） and optical microscopy （OM）. The mechanical properties and corrosion resistance were measured. The results show that the as-cast microstructure of magnesium alloy can be greatly refined under high pressure. The average length of primary arm was about 165 μm and the secondary arm spacing was around 35 μm. When the solidification pressure was up to 2 GPa, the average size of primary was down to 50 μm and the secondary arm spacing was 8 μm. When the solidification pressure was up to 4 GPa, the average length of primary arm and secondary arm spacing were 20 μm and 5μm respectively. The network of the second phase was gradually split and tends to become granular under the pressure of 4 GPa. The compressive strength of experimental alloy was increased from 346 MPa in conventional casting to 446 MPa under 4 GPa. In 3.5 % medium of NaCl, the high pressure solidification alloy has a smaller corrosion current density and a more positive corrosion potential.