轧制温度对7075铝合金组织演变及力学性能影响

Effect of Rolling Temperatures on Microstructure Evolution and Mechanical Properties of 7075 Aluminum Alloy

摘要:

铝合金作为非钢质结构材料，在地质勘探、石油开采和科学钻探等领域的深井钻探中得到广泛应用。随着大陆及海洋深部油气钻探需求日益增加，对钻探装备和工具的综合性能提出了更高的要求。高强度铝合金以高比强度、低刚度和高耐腐蚀性能等显著优点，已在大位移井、定向井和超深井钻探中得到广泛应用。然而，目前对钻杆用7075超硬铝合金的热加工性能缺乏系统研究。为解决该问题，对7075铝合金在不同轧制温度下的组织演变和力学性能进行了系统地分析和研究。通过光学显微镜和X射线对合金晶粒尺寸和第二相的分布情况进行了观察分析，利用万能试验机对合金的抗拉强度和断裂延伸率等力学性能进行了研究。结果表明，随着轧制温度的升高，7075铝合金的组织和力学性能均会发生显著变化。在轧制温度250—350 ℃范围内，7075铝合金晶粒尺寸先增大后减小，晶粒当量直径平均值从215 μm增加至257 μm，后又减小至220 μm；当轧制温度为400 ℃时，合金的晶界组织不明显，原始粗大晶界逐步消失，出现了细小球状晶粒且当量直径平均值减小至47 μm。抗拉强度结果表明，随着轧制加工温度从250 ℃升高到400 ℃时，7075铝合金的抗拉强度变化的趋势为先减小后增大。当轧制温度为350 ℃时抗拉强度达到最低值521 MPa，当轧制温度为400 ℃时抗拉强度达到最大值570 MPa。此外，高的轧制温度（400 ℃）能显著增强7075铝合金的强度和塑性。拉伸断口的SEM图像显示，轧制温度400 ℃时，7075铝合金样品的断裂方式从偏脆性断裂变为偏韧性断裂。因此，轧制温度400 ℃被认为是7075铝合金适宜的热轧加工温度。本研究为不同轧制温度对轻质高强7075铝合金的力学性能影响规律提供了理论支撑。

Abstract:

Aluminum alloy is the most widely used non-steel structural material. Increasing drilling depths in geological exploration， oil exploitation and scientific drilling a impose higher requirements on the performance of drilling equipment and tools. High strength aluminum alloy materials， known for their high specific strength， low stiffness， and high corrosion resistance， have been extensively used in the design of drill strings for extended reach wells， directional wells and ultra-deep wells. However， there is a lack of systematic research on the optimal hot working temperature of 7075 superhard aluminum alloy used in drill pipe. In this paper， the microstructure evolution and mechanical properties of 7075 aluminum alloy were studied at different rolling temperatures such as 250 ℃， 300 ℃， 350 ℃ and 400 ℃. The grain size and second phase were analyzed by optical microscopy and X-ray diffraction， while the tensile strength and fracture elongation were measured using a universal testing machine. The results show that the microstructure and mechanical properties of 7075 aluminum alloy change with the increase of rolling temperature. Within the 250 ℃ to 350 ℃ range， the grain size initially increases and then decreases as rolling temperature rises， with the average grain equivalent diameter increasing from 215 μm to 257 μm， and then decreasing to 220 μm. At 400 ℃， grain boundaries becomes less distinct， original coarse grain boundaries gradually disappear， and fine spherical grains emerge， reducing the average equivalent diameter decreases to 47 μm. Additionally， as the rolling temperature increased from 250 ℃ to 400 ℃， the tensile strength of 7075 aluminum alloy first decreased and then increased， reaching the a minimum of 521 MPa at 350 ℃ and a maximum of 570 MPa at 400 ℃. The strength and plasticity of 7075 aluminum alloy were enhanced at 400 ℃. The SEM images of tensile fracture also show that the fracture mode of 7075 aluminum alloy sample shifts from brittle to ductile at 400 ℃. Therefore， a rolling temperature of 400 ℃ is identified as the optimal hot rolling processing temperature for 7075 aluminum alloy.