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采用激光熔化沉积技术制备了4045铝合金薄壁试样,研究了沉积试样热处理前后的显微组织演化,并测试其显微硬度。结果表明,沉积试样显微组织具有定向快速凝固特征,由Al枝晶和Al-Si共晶组成,其一次枝晶间距约22.3μm,二次枝晶间距约7.5μm,体积分数约42.7%,沉积试样顶部出现柱状树枝晶向等轴树枝晶转变。当前沉积层从底部到顶部冷却速度的降低导致Si相从珊瑚形貌向片状形貌转变,足够高的重熔率能保证后续沉积层重熔掉当前沉积层顶部片状Si相,以获得变质效果良好的珊瑚形貌Si相,热影响作用使紧邻熔合线过热区的珊瑚形貌Si相发生粗大等轴粒状化,导致其显微硬度低于层内区。珊瑚形貌Si相在540℃等温热处理保温20 min即可完成粒状化,并且随着保温时间延长,Si相发生粗化长大,显微硬度下降。
The 4045 aluminum alloy thin wall samples were prepared by laser melting deposition technology. The microstructure evolution of the deposited samples before and after heat treatment was studied and the microhardness was tested. The results show that the microstructures of the deposited samples have the characteristics of rapid solidification and consist of Al dendrite and Al-Si eutectic. The first dendrite spacing is about 22.3μm, the second dendrite spacing is about 7.5μm, the volume fraction is about 42.7% At the top of the deposited sample, there appeared columnar dendrite to equiaxed dendrite transformation. The current cooling rate of the deposited layer decreases from bottom to top, which leads to the transformation of Si phase from coral morphology to flaky morphology. The high enough remelting rate ensures that the subsequent deposition layer remelts the flaky Si phase of the top of the current sedimentary layer to obtain The degenerative effect of coral morphology of Si phase, the thermal effect of the superconducting area near the weld line coral morphology coarse co-axial Si phase granulation, resulting in its lower hardness than the inner layer. Co-morphology Si phase isothermally treated at 540 ℃ for 20 min to complete the granulation, and with the holding time, Si phase coarsening and growth, decreased microhardness.