压力对铸造Al-Li-Cu合金组织和力学性能的影响

Effect of pressure on macro-/micro- structures and mechanical properties of Al-Li-Cu cast alloy

采用直接挤压铸造工艺制备一种密度为2.525 g/cm3的A1-2.47Li-1.49Cu合金铸锭,通过宏观腐蚀、OM、DSC、SEM、XRD及拉伸性能测试等手段对其组织和力学性能进行研究。结果表明:压力作用下凝固可以显著改善铸锭的表面质量,获得致密无缩松缺陷的铸锭,50 MPa下,铸锭中的柱状晶平均长度较重力铸造下的减小20%;合金铸态微观组织主要由初生α(Al)、T2相以及少量AlLiSi和Al6(CuFe)组成,施加压力不改变相的组成,但可使第二相尺寸更小,分布更均匀;合金硬度、抗拉强度以及伸长率均随压力增大而增大,但50 MPa以后压力对性能的影响不明显。50 MPa下T5热处理的合金抗拉强度为329 MPa,伸长率为6%,硬度为135HBS,较重力铸造合金分别提高了7.2%、107%和3%。

Al-2.47Li-1.49Cu alloy ingot with density of 2.525 g/cm3 was prepared by direct squeeze casting. The macro-and micro-structures and mechanical properties of the alloy were analyzed by macro corrosion, OM, DSC, SEM, XRD and tensile properties test. The results indicate that pressure can not only improve the surface quality and refine columnar areas, but also eliminate the porosity to obtain the dense ingot. The average length of columnar grains obtained at applied pressure of 50 MPa is 20% shorter than that of the gravity alloy cast. The microstructure of the as-cast alloys mainly consists of primaryα（Al）, T2 and a small amount of AlLiSi and Al6（CuFe） phases. The applied pressure does not change the phase composition, but makes them smaller and more uniform. In addition, the microhardness, tensile strength and elongation of the alloy increase with increasing the pressure, but the applied pressure does not affect the mechanical properties obviously when the pressure exceeds 50 MPa. The T5 heat-treated alloy prepared under 50 MPa can reach a level of ultimate tensile strength of 329 MPa, elongation of 6%and microhardness of 135HBS, which are 7.2%, 107%and 3%, respectively higher than those of the gravity cast alloy.