Product Code: PIC2008_1108

Laser Peening of 7050 Aluminum Alloy with Fastener Holes
Authors:
Zou Shikun, BAMTRI; Beijing Peoples Republic of China
Ziwen Cao, Beijing Aeronautical Manufacturing Technology Research Institute ; Beijing Peoples Republic of China
Shuili Gong, Beijing Aeronautical Manufacturing Technology Research Institute ; Beijing Peoples Republic of China
Presented at PICALO 2008

In order to develop the application of laser shock processing (LSP) as a strengthening technology for 7050 aluminum alloy fasten holes, the fatigue properties of laser shock-processed aluminum alloy specimens were investigated. At first, we characterized and compared the dislocation density and surface residual stress induced in the shock-effect zone with that of the base material. Then, the fatigue specimens with stress-concentration hole (notch) were treated by LSP. The fatigue life of LSP-treated specimens were measured and compared with that of specimens made from base material without LSP. Fatigue tests were taken under special flight spectrum loading condition for mid-airframe. Our results indicate that laser peening improves the fatigue life of all specimens tested today. Specimens treated by LSP before hole-drilling is shown to have longer fatigue life than specimens treated by LSP after hole-drilling. At last, we investigated the difference of both sequences by analyzing the plastic strain and residual stress induced by LSP. It is evident that LSP induces both plastic strain and deformation at the surface layer. The plastic strain induced by LSP is shown to produce harmful orifices with sharp-angle near the edge of hole. The residual stress induced by LSP appears to remain compressive even after the hole-drilling process. In average, the fatigue life of specimens treated by LSP before hole-drilling is found to be 173% longer than that of untreated samples and is approaching the life enhancement factor demonstrated by rod extrusion method (on specimens with large diameter holes).