Microstructural evolution and mechanical behaviors of Al-Cu-Li alloy processed by laser shock peening

Abstract

The effects of laser shock peening (LSP) on the mechanical behaviors of 2198 Al-Li alloy with two different temper conditions (T6 and T8) were investigated through tensile tests and microhardness measurements. Moreover, the microstructural response of the samples under T6 condition, T8 condition, T6 followed by LSP treatment (T6 + LSP) and T8 followed by LSP treatment (T8 + LSP) were also examined by TEM. Experimental results exhibited that the mechanical properties were strengthened by T8 + LSP treatment. Namely, both the tensile strength, microhardness and elongation increased simultaneously under T8 + LSP condition, which received an increase of 23.1%, 61.2% and 3.9% contrast to the T6 condition sample (126.4 HV, 458.5 MPa and 12.9%). The tested results revealed that LSP can also introduce residual compressive stress on the alloy surface. Furthermore, microstructural analysis suggested that high-density dislocations were produced near the precipitates and the compressive residual stress was also formed near the shocked surface. The precipitation strengthening was a primary mechanism for the T6 condition sample. The enhanced mechanical properties of T8 condition sample were mainly ascribed to the increased number density of dislocations and precipitates induced by 3% pre-stretching. A pronounced strengthening effect by T8 + LSP treatment was appreciable due to the comprehensive results of the grain refinement and the interaction between high-density dislocations and precipitations.