超声滚压强化7075铝合金工件表面性能的研究

Surface Properties of 7075 Aluminum Alloy Workpieces after Ultrasonic Burnishing Processing

目的探究超声滚压强化技术对7075铝合金工件表面性能的影响。方法对7075铝合金棒状试样精车加工后进行了超声滚压强化处理。综合使用粗糙度测量仪、表面显微硬度仪、金相显微镜以及X射线衍射应力分析仪,研究了处理前后工艺参数中的压下量对试样的表面粗糙度、表面显微硬度、表面微观组织及表面残余应力等表面性能的影响。结果超声滚压强化处理后,试样表面粗糙度由0.976μm降低至0.047μm,表面显微硬度由105.6HV0.2提高至119HV0.2,显微硬度提高了15%。精车加工后,精车试样的表层组织与心部组织几乎无变化。超声滚压强化后,相对心部组织而言,表层晶粒组织得到显著细化,表层均为残余压应力,压应力深度为1.75 mm。残余压应力最大值位于最表层,最大为-174.0 MPa,且距离最表层越远,残余压应力总体呈减小趋势。结论通过对比研究精车试样与超声滚压试样,发现超声滚压强化工艺可以大大地降低试样表面粗糙度,显著地细化表层试样晶粒与提高表面硬度,改善残余应力的分布,并引入一定深度的残余压应力。

The work aims to explore effects of ultrasonic burnishing（UB） technology on surface properties of 7075 aluminum alloy workpieces. Finish turning and ultrasonic burnishing were applied to rotating bar specimens made from 7075 aluminum alloy successively. Effects of rolling reduction among process parameters on surface properties of the specimens including surface roughness, surface microhardness, surface microstructure and surface residual stress were investigated with roughness tester, microhardness tester, metalloscope and X-ray diffraction stress analyzer before and after the finish turning and UB. After finish turning, surface roughness of the specimens decreased from 0.976 μm to 0.047 μm, surface microhardness of the specimens increased from 105.6 HV0.2 to 119 HV0.2（increased by 15%）. After UB, surface grain of the specimens was approximate the same as that of the central grain. The surface grain of the UB specimens was considerably refined compared to the central grain after UB. Residual compressive stress was all induced on the surface layer, the maximum value appeared on the surface and the residual compressive stress layer was 1.75 mm deep. The residual compressive stress on the top surface was up to-174.0 MPa, but it tended to decrease as a whole as distance from the top surface increased. By comparing the specimens receiving finish turning and UB, it can be concluded that UB can remarkably reduce surface roughness of the specimens, dramatically refine surface grain, noticeably improve surface microhardness, improve distribution of residual stress and introduce certain depth of residual compressive stress.