稀土Ho对ZA52合金显微组织及力学性能的影响

摘要

采用OM、XRD、SEM、EDS和高温拉伸试验机研究了不同Ho含量对ZA52合金的微观组织与力学性能的影响.结果表明,加入Ho能够细化基体组织,使Mg32 (Al,Zn)40相由半连续网状结构转变为孤岛状或颗粒状,同时会生成花瓣状和块状的Al2Ho相.当Ho含量超过0.5％时,花瓣状Al2Ho逐渐消失,块状相逐渐增多,随着Ho含量的增加,常温和高温下的抗拉强度和伸长率都有了显著的提高.其中添加Ho含量为1.5％时,常温抗拉强度σb和伸长率δ达到最大值分别为234.3 MPa、13.6％.高温抗拉强度σb为117.5 MPa,高温伸长率无明显变化.加Ho后的合金200℃下断裂方式属于以韧性为主的准解理断裂和韧窝断裂的混合断裂形式.%In this paper, the effects of Ho content on microstructure and mechanical properties of ZA52 magnesium alloy have been investigated by using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and various testing machines. The results indicate that the addition of Ho not only suppresses the formation of Mg32 (Al, Zn)49 phase and modifies the T-Mg32 (Al, Zn)49 phase but also refines the grains of the ZA52 alloy. Furthermore, new phases are formed in the forms of petal-like and graininess shape, which are verified as A12Ho phase. When the addition of Ho is more than 0.5%, petal-like phase gradually disappeared, meanwhile the precipitates gradually increased. The addition of Ho to the ZA52 alloy improves the tensile properties at room temperature and 200 ℃ remarkably, especially with the addition of 1.5% Ho. The maximum tensile strength and elongation are obtained in ZA52 alloy, and the values are 243.3 MPa, 13.6% respectively at room temperature. The tensile strength is 117.5 MPa and the elongation does not change significantly at 200 ℃. The fracture mechanism of ZA52+Ho alloy at 200 ℃ is a mix of quasi-cleavage fracture and dimple fracture.