目的 针对铸态7075铝合金组织偏析严重、力学性能差、难以达到汽车产品应用要求的问题,通过固溶时效处理改善合金的偏析组织与力学性能,以满足汽车产品的应用要求。方法 以铸态7075铝合金为研究对象,分别进行单级固溶+人工时效（T6）和双级固溶+人工时效（T6）处理。采用光学显微镜（OM）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）和X射线衍射（XRD）分析不同热处理制度下合金的微观组织与相组成演变,采用电子万能试验机测试合金的室温拉伸力学性能并观察断口形貌,系统研究固溶时效制度对铸态7075铝合金显微组织与力学性能的影响规律。结果 铸态7075铝合金组织主要由α-Al基体、MgZn2相及Al2CuMg相组成,存在明显偏析。经单级固溶T6处理后,合金主要相为α-Al相、MgZn2相和Al2CuMg相,二次相在晶界交汇处呈球状和杆状析出,平均直径约23 nm。经双级固溶T6处理后,XRD图谱中仅出现α-Al相和Al2CuMg相的衍射峰,MgZn2相基本固溶于基体;晶界与晶内的球状、杆状二次相明显减少,颗粒状相增多并有长大趋势,少量呈方块状。在时效过程中,Al2CuMg相通过消耗MgZn2相而持续形核长大,体积分数增加,平均直径增至约44.5 nm。力学性能测试结果表明,双级固溶T6合金抗拉强度达647.2 MPa,屈服强度为605.2 MPa,断裂韧度为41.7 MPa·m1/2,伸长率为8.76%;拉伸断口由沿晶脆性断裂转变为穿晶韧性断裂,断口表面分布大量韧窝。结论 双级固溶T6处理较单级固溶T6处理能更充分地消除铸态7075铝合金的偏析,促进MgZn2相固溶、细化并均匀化二次相,从而显著提升合金的综合力学性能（抗拉强度647.2 MPa、屈服强度605.2 MPa、伸长率8.76%、断裂韧度41.7 MPa·m1/2）,断裂方式由沿晶脆性断裂转变为穿晶韧性断裂。经双级固溶+人工时效处理后,铸态7075铝合金的力学性能可满足汽车产品的应用要求,为该合金在汽车结构件领域的应用提供了工艺依据。
Abstract
Owing to the severe segregation in the microstructure and the poor mechanical properties of the as-cast 7075 aluminum alloy, which fail to meet the application requirements of automotive products, the work aims to improve the segregated microstructure and mechanical properties of the alloy through solution and aging treatment, so as to satisfy the application requirements of automotive products. The as-cast 7075 aluminum alloy was adopted as the research object, and both single-stage solution + artificial aging (T6) and two-stage solution+artificial aging (T6) treatments were conducted. Optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to analyze the evolution of the microstructure and phase constituents of the alloy under different heat treatment regimes. An electronic universal testing machine was used to evaluate the room-temperature tensile mechanical properties and to observe the fracture morphology. The effect of the solution and aging treatment regimes on the microstructure and mechanical properties of the as-cast 7075 aluminum alloy was systematically investigated. The as-cast 7075 aluminum alloy was mainly composed of an α-Al matrix, MgZn2 phase and Al2CuMg phase, with pronounced segregation. After single-stage solution T6 treatment, the main phases of the alloy were α-Al, MgZn2 and Al2CuMg, and the secondary phases precipitated at grain boundary triple junctions with spherical and rod-like morphologies, exhibiting an average diameter of approximately 23 nm. After two-stage solution T6 treatment, only the diffraction peaks of the α-Al and Al2CuMg phases appeared in the XRD patterns, indicating that the MgZn2 phase was essentially dissolved into the matrix. The spherical and rod-like secondary phases at grain boundaries and within grains decreased remarkably, while granular phases increased with a tendency to coarsen, and a small amount exhibited a blocky morphology. During aging, the Al2CuMg phase continuously nucleated and grew by consuming the MgZn2 phase, leading to an increase in its volume fraction and a growth in the average diameter to approximately 44.5 nm. Mechanical property tests demonstrated that the alloy after two-stage solution T6 treatment achieved an ultimate tensile strength of 647.2 MPa, a yield strength of 605.2 MPa, a fracture toughness of 41.7 MPa·m1/2 and an elongation of 8.76%. The tensile fracture transformed from intergranular brittle fracture to transgranular ductile fracture, with a large number of dimples distributed on the fracture surface. Compared with the single-stage solution T6 treatment, the two-stage solution T6 treatment can more thoroughly eliminate the segregation of the as-cast 7075 aluminum alloy, promote the dissolution of the MgZn2 phase, and refine and homogenize the secondary phases, thereby significantly improving the comprehensive mechanical properties of the alloy (ultimate tensile strength of 647.2 MPa, yield strength of 605.2 MPa, elongation of 8.76%, and fracture toughness of 41.7 MPa·m1/2), and changing the fracture mode from intergranular brittle fracture to transgranular ductile fracture. After the two-stage solution plus artificial aging treatment, the mechanical properties of the as-cast 7075 aluminum alloy can satisfy the application requirements of automotive products, which provides a process basis for the application of this alloy in automotive structural components.
关键词
7075合金 /
热处理 /
显微组织 /
力学性能 /
断裂韧性
Key words
7075 alloy /
heat treatment /
microstructure /
mechanical properties /
fracture toughness
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