Improved Surface Integrity and Service Performance of Al-Li Alloy 2A97 Via Shot Peening Process with Various Coverages

Compared with traditional Al alloys, Al-Li alloys with the lower density are widely used in aerospace and transportation fields. However, the limited mechanical strength restricts their further application. In this study, to realize the surface strengthening and modification of Al-Li alloy 2A97, shot peening operations with various coverages are performed. The influence of the coverage upon surface integrity and further service behaviors of alloy 2A97 is investigated. The shot peened surface integrity, including surface roughness, residual stress, microhardness, and microstructure are measured and characterized. Then friction-wear and scratch tests are carried out to evaluate the wear resistance and surface coating adhesion strength. It is found that the surface integrity of alloy 2A97 is dramatically changed. Refined grains, residual compressive stress and microhardness with high magnitude are generated within shot peened surface deformed layers. They contribute to the improved wear behavior, while the enhanced adhesion strength is mainly attributed to residual stress and surface roughening. When shot peening coverage increases from 0 to 600%, the shot peened surface roughness, residual stress, microhardness, along with the depth of plastic deformation layer all enlarge. When the coverage exceeds 600%, all measurements tend to saturation values. Due to the over-peening phenomenon, severe defects, i.e. microcracks, appear on the shot peened surface with 800% coverage. It exactly account for the poorer wear property and lower adhesion strength than the surface with 700% coverage, although the stress and microhardness are almost the same for the two surfaces. These findings can promote the wider range of applications of Al-Li alloys.