Papers by Author: Kai Yu Luo

Abstract: The ultra-high plastic deformation behavior by laser shock processing on the LY12 aluminum alloy had been investigated. The morphology of the materials had been analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the grain refinement layer was formed in the thickness of about 100μm .The dislocation density of LY12 aluminum alloy should be large increased after laser shocking because the accumulation of dislocation was appeared on the grain boundary. With the laser energy density increased there formed subgrain structure and eventually generate ultra-fine grain. Hardness test results also show that the surface hardness obtains a big growth about 60% after laser shock processing. The results showed that the formation of ultra-high plastic strain can improve the surface hardness of LY12 aluminum alloy, and thus effectively improve the comprehensive mechanical properties.

Abstract: The strain-rate sensitivity of LY2 aluminum (Al) alloy subjected to laser shock processing (LSP) was investigated according to the fracture morphology at strain-rates ranging from 0.00001 s-1 to 0.1 s-1. The fracture morphology was observed by the scanning electron microscopy (SEM). Fracture morphology at different strain-rates suggested that LY2 Al alloy after LSP seemed to evolve towards a more ductile dimple fracture mode with increasing the strain-rates. The relations underlying the fracture morphology and strain-rate sensitivity were also addressed.

Abstract: In the present investigation, the effects of processing parameter on three-point bending fatigue pergormance of TC4 alloy are examined, particular emphasis is devoted to the question of appropriate LSP processing parameters for improving the fatigue properties. Based on cyclic deformation and stress/life (S/N) fatigue behavior, it was found that there was the optimal shock number of overlapped spots for three-point bending fatigue pergormance of TC4 alloy. By comparing with the as-received specimen, the fatigue performance of TC4 alloy has the most obvious improvement by LSP with two impacts.

Abstract: Laser shock processing (LSP, also known as Laser shock peening) is applied by using a high energy pulsed laser to create a high amplitude stress wave or shock wave on the surface to be treated. LSP is proved to be superior to conventional treatments such as shot peening in many engineering products. This paper focuses on Laser shock processing and its effects on mechanical properties of material AISI 8620 alloys steel. Experiment results indicated that compared with base material, the surface hardness increased by 13.8%, and compressive residual stress increased by 521%. Statistical method was introduced to analyze hardness and residual stress change before and after the LSP.

Abstract: The surface of Al2O3 coating sprayed on 40Cr substrate was re-melted with high power continuous CO2 laser, and its micro-hardness and residual stresses were measured, respectively. The strengthening mechanism of Al2O3 coating by laser re-melting was analyzed and discussed. The experimental results shown that the surface of Al2O3 coating by laser re-melting is neat and smooth, and its compositions are even, its structures are compact, and Al2O3 coating is evenly distributed in its surface with grain forms, and its micro-hardness increases about 200%; Residual stress of Al2O3 coating by laser re-melting is changed into compressive stress from tensile stress, which is benefit to improving bonding strength of coating-substrate interface.

Abstract: The large area delaminated (two layers) and non-delaminated samples of 1mm-thick aluminium alloy 2024 were shocked by pulse laser, the restricted layer and the absorbing layer were coated on the surface of the samples, and the PVDF sensors were set on the facing of a quilt of the samples. The signs of laser shock waves were transmitted to the computer by the oscillograph. The results indicated that can be effective detected by laser shock waves, and the math model of hierarchical sheet-metal by laser shock wave was fundamentally developed. A new method to detect the large area delaminated samples was provided, which has the definite engineering importance.

Abstract: The marking system by laser shock wave (LSW) based on liquid crystal mask, which differs entirely from marking by laser ablation (or laser thermal effect), was established. Two-dimension (2D) nondestructive markings based on liquid crystal mask were prepared by LSW, and the distribution of residual stresses in laser-shocked region was measured and analyzed. The results showed that tensile residual stresses of sample surface were converted into compressive residual stresses by LSW, which is a nondestructive marking for aviation key parts.