J.W. Zhong

Effects of Laser Shock Processing on Mechanical Properties of Laser Welded ANSI 304 Stainless Steel Joint

With the rapid development of engineering component with integration, high-speed and multi-parameter, traditional techniques haven’t met practical needs in extreme service environment. Laser welding, a new welding technology, has been widely used. However, it would generate the drop of mechanical properties for laser welded joint due to its thermal effect. Laser shock processing (LSP) is one of the most effective methods to improve the mechanical properties of laser welded ANSI 304 stainless steel joint. In this paper, the effects of LSP on the mechanical properties of laser welded ANSI 304 stainless steel joint have been investigated. The welded joint on the front of the tensile samples is treated by LSP impacts, and the overlapping rate of the laser spot is 50%. The tensile test of the laser welded joint with and without LSP impacts is carried out, and the fracture morphology of the tensile samples is analyzed by scanning electron microscope (SEM). Compared with the yield strength of 11.70 kN, the tensile strength of 37.66 kN, the yield-to-tensile strength ratio of 0.310 7, the elongation of 25.20%, the area reduction of 32.68% and the elastic modulus of 13 063.876 MPa, the corresponding values after LSP impacts are 14.25 kN, 38.74 kN, 0.367 8, 26.58%, 42.29% and 14 754.394 MPa, respectively. Through LSP impacts, the increasing ratio of the yield strength and tensile strength are 121.79% and 102.87%, respectively; the elongation and area reduction are improved by 5.48% and 29.38%, respectively. By comparing with coarse fracture surface of the welded joint, the delamination splitting with some cracks in the sharp corner of the welded joint and asymmetric dimples, LSP can cause brighter fracture surface, and finer and more uniform dimples. Finally, the schematic illustration of dimple formation with LSP is clearly described. The proposed research ensures that the LSP technology can clearly improve the yield strength, tensile strength, yield-to-tensile strength ratio, elongation, area reduction and elastic modulus of the welded joint. The enhancement mechanism of LSP on laser welded ANSI 304 stainless steel joint is mainly due to the fact that the refined and uniform dimples effectively delay the fracture of laser welded joints.

Effects of processing parameters on fatigue properties of LY2 Al alloy subjected to laser shock processing

We address the effects of processing parameters on residual stresses and fatigue properties of LY2 Al alloy by laser shock processing (LSP). Results show that compressive residual stresses are generated near the surface of samples due to LSP. The maximum compressive residual stress at the surface by two LSP impacts on one side is higher than that by one LSP impact. The maximum value of tensile residual stress is found at the mid-plane of samples subjected to two-sided LSP. Compared with fatigue lives of samples treated by single-sided LSP, lives of those treated by two-sided LSP are lower. However, these are higher than untreated ones.

Effect of Strain-Rate on the Fracture Morphology of LY2 Aluminum Alloy by Laser Shock Processing

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.

Experiment of Laser Shock Processing on AISI 8620 Alloy Steel

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.

Investigation on Fatigue Performance of TC4 Alloy by Laser Shock Processing with Different Processing Parameters

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.