铝锂合金高速铣削表面完整性实验研究

铝锂合金密度低、比强度高、比刚度高等优良特性使得其成为新一代航空航天飞行器的主要结构材料.飞机蒙皮作为维持飞机外形的主要结构件,在飞机起飞降落过程中承受舱内外压差变化所引起的交变载荷作用,因此对于蒙皮结构零件的疲劳强度要求十分苛刻.零件的疲劳裂纹萌生往往是从表面的微观缺陷开始,并且表层以及亚表层的力学状态将影响裂纹萌生以及扩展速度.表面完整性包括表面的几何轮廓、显微硬度、金相组织、残余应力等,这些因素综合影响着零件的疲劳性能.与此同时,表面完整性表征参数与被加工材料属性、热处理状态以及加工工艺等具有密切的联系.研究了铝锂合金的机械铣削加工工艺对于其表面完整性的影响.传统蒙皮结构加工往往采用化学铣削的方法进行,占用厂房面积大,污染严重,废液处理费用高等,不符合现代可持续绿色制造的理念.目前对于铝锂合金的超塑成形工艺研究较多却鲜见有相关铝锂合金切削表面完整方面的相关研究.研究在干切情况与液氮冷却情况下切削三要素以及上一道滚压工艺对于表面完整性的影响,通过正交试验的方法全面考察了工艺参数对于表面形貌各个指标、表层亚表层金相组织以及残余应力的影响权重,并且验证了其显著性.比较了干切与液氮低温切削情况下表面形貌以及残余应力状态的异同点,验证了液氮冷却切削对于铝锂合金表面完整性提升的有效性,为提高铝锂合金疲劳性能提供了实验依据.

Investigation of surface integrity of aluminum lithium alloy in high speed machining

Aluminum-lithium alloy takes the advantage of low density, high specific strength and specific stiffness that make it the candidate for the structural material in the new generation of aerospace vehicles. Aircraft skin is under the cabin pressure changes caused by alternating loads while the aircraft taking off and landing, so the fatigue strength of structural components is very important. Structural fatigue crack initiates from the surface of microscopic defects, and surface and subsurface mechanical state affects the crack initiation and propagation speed. The surface integrity includes surface contours, micro-hardness, microstructure, residual stress, etc. These factors affect the fatigue performance of the structure. Meanwhile, the surface integrity associates with the material character, machining parameters, and heat treatment process. This paper studies the surface integrity of aluminum- lithium alloy in mechanical milling process. Traditional skin structures are obtained using chemical machining methods, by which the plant occupy large area with serious pollution and the waste disposal costs higher. At present, studies on superplastic forming process of aluminum-lithium alloys are carried out extensively and those on surface integrity of aluminum-lithium alloy in cutting process are very lacking. In this paper we investigate the contributions of machining parameters and the previous rolling process on the surface integrity of aluminum-lithium alloy with liquid nitrogen and dry cutting conditions. Also we give the comparison of the surface topography as well as the residual stress in liquid nitrogen and dry conditions. The experiment results verify the enhancement of surface integrity of aluminum-lithium alloy in liquid nitrogen condition, which supplies the experimental basis for the improvement of the fatigue properties of aluminum-lithium alloy by using the mechanical milling process.