中断时效对7075铝合金切削表面质量及刀具磨损影响研究

Effect of Interrupted Aging on Cutting Surface Quality and Tool Wear of 7075 Aluminum Alloy

目的探究中断时效工艺对7075铝合金切削加工性能的影响,为中断时效工艺对材料切削加工性能的改善提供理论依据。方法选取仅进行T6时效处理的试样作为对照组,通过扫描电镜(SEM)、X射线衍射仪(XRD)等手段对已加工表面质量、切削力及刀具磨损进行分析。结果经不同时效处理后,7075铝合金的主要析出相为η(MgZn_(2))相,且相较于T6热处理工艺的7075铝合金,7075-T6I4铝合金表现出更高的衍射峰强度及更大的半高宽。在不同的时效处理条件下,表面粗糙度Ra均与切削速度呈负相关关系,而与切削深度、进给量呈正相关关系,仅T6时效处理时,表面粗糙度Ra随切削深度的增大呈先增大后减小再增大的变化趋势,在不同切削速度下,与T6时效处理相比,T6I4中断时效处理的表面粗糙度Ra最大降低了5.8%,而在不同切削深度和进给量下最大降低了1.9%和17.1%,且工件表面主要存在切屑黏附、微裂纹以及微孔洞等缺陷;切削力在切削速度为500~750m/min时呈增大趋势,随后又逐渐减小,然而与切削深度、进给量之间则呈正相关关系,仅经T6I4中断时效处理后的y向切削力在进给量为0.06~0.08 mm/z时逐渐减小,随后呈增大的变化趋势。增大切削速度以及减小进给量均可有效改善刀具磨损程度,且在切削过程中刀具磨损形式主要表现为崩刃和黏结磨损。结论与T6时效处理相比,T6I4中断时效处理表现出更好的表面质量、更小的切削力及更轻的刀具磨损,较大的切削速度和较小的进给量、切削深度有助于提高7075铝合金的切削加工性。

7075 aluminum alloy is widely used in the aerospace field for main load bearing structural parts because of its high specific strength and specific stiffness and good corrosion resistance.The overall"hollowing"process is often used.Due to the large size,thin wall and easy deformation of the overall structural parts,there is a risk of fatigue fracture in the face of the complex service environment.The selection of the appropriate aging treatment can often improve the cutting surface integrity and mechanical properties of the material and increase its fatigue life.In this paper,7075 aluminum alloy was firstly subject to T6I4 interrupted aging treatment,with T6 continuous aging treatment as the control group.The machined surface and tool wear morphology were characterized by an X-ray diffractometer(SX-27mini)and a scanning electron microscope on the machined specimens after aging.The effect of interrupted aging on the surface integrity of machined 7075 aluminum alloy was investigated.The results showed that the main precipitated phase of 7075 aluminum alloy after T6 and T6I4 aging treatment wasη(MgZn_(2))phase.The position of the main peak of the diffraction of the T6 aluminum alloy specimen(111)was 38.51°at the same cutting parameters.In contrast,the T6I4 aluminum alloy specimen(111)diffracted the main peak position of 38.22°,which shifted toward the direction of the lower diffraction angle.The half-height width of the diffraction peak of the XRD pattern of the 7075 aluminum alloy with T6I4 interrupted aging was larger than that of the T6 aging treatment,introducing a larger residual compressive stress.The surface roughness was negatively correlated with the cutting speed,and positively correlated with the cutting depth and feed rate,only the T6 aluminum alloy showed a trend of increasing,then decreasing and then increasing with the increase of cutting depth.The surface roughness of T6I4 interrupted aging treatment at different cutting speeds was 5.8%lower than the maximum of T6 aging treatment,while the maximum reduction was 1.9%and 17.1%at different cutting depth and feed rate.And the surface of the workpiece mainly had defects such as chip adhesion,micro-cracks and micro-porosity.The cutting force showed a trend of increasing and then decreasing with the increase of cutting speed,and the minimum cutting force was 361.021 N when the cutting speed was 1000 m/min.The cutting force was positively correlated with the cutting depth and feed rate,and only the Y-directional cutting force of T6I4 aluminum alloy showed a trend of decreasing and then increasing with the increase of feed rate.Increasing the cutting speed and reducing the feed rate could effectively improve the tool wear,and in the cutting process tool wear was mainly in the form of chipping and bonding wear.In summary,T6I4 interrupted aging shows better surface quality,less cutting forces and less tool wear compared with T6 continuous aging treatment.And the larger cutting speed and smaller feed rate and cutting depth help to improve the machinability of 7075 aluminum alloy.