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

Abstract

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.