位错及其运动在航空铝合金激光冲击表面改性中的作用

Effect of dislocation and its motion on surface modification of aero-aluminum alloy by laser shock processing

利用输出波长为1064 nm的钕玻璃YAG激光器,对2000系铝铜镁航空铝合金进行了激光冲击表面改性试验。用TEM和IFFT方法分析了位错及其运动在铝合金激光冲击表面改性中的作用。结果表明,激光冲击表面改性效果明显,可使表层硬度提高50%以上;残余压应力达到120 MPa以上。激光冲击在基体中诱发大量位错,位错组态主要包括刃型位错、异号位错组和由位错偶构成的螺型位错等。合金中的析出相与基体中的应变位错保持半共格关系,增强了析出相颗粒的强化作用;激光冲击的超高应变率导致基体产生有序连续排列的同号位错形成位错墙,将基体分割为纳米级亚晶粒。激光冲击诱发的复杂位错组态是表层硬度和残余应力提高的内在原因。

An A1-Cu-Mg aero-aluminum alloy was laser shocked by using the Nd： YAG laser setup with the 1064 nm output wave length. The effect of dislocations and their motion on the surface modification of the aluminum alloy was analyzed via the TEM and IFFT method. The results indicate that the surface hardness of the alloy by laser shock processing （LSP） can be increased by 50% , the residual compressive stress reaches 120 MPa. TEM and IFFT analysis of microstructure demonstrates that large number of dislocations are induced in the laser shocked matrix, mainly including edge dislocations, dislocation group with different signs; and screw dislocations consisting of dislocation dipoles. The precipitates are semi-coherent relations with the induced dislocations by LSP, which enhance their strengthening effect. The matrix of the alloy can be refined into nano-crystalline sub-grains by dislocation walls constructed by the ordered dislocations with the identical signs induced by the ultra-high strain rate of LSP. Therefore, the complex dislocation configuration caused by LSP is responsible for the improvement of surface hardness and compressive residual stress state.