Residual Stress Distribution and Microstructure Evolution of AA 6061-T6 Treated by Warm Laser Peening

Abstract

Abstract:The aim of this paper is to study the effects of laser peening (LP) on the residual stress distribution and microstructure evolution of AA 6061-T6 under different temperatures. A laser peening experiment was conducted on the square-shape samples by using single spot and 50% overlap shock. Three-dimensional surface morphologies of treated samples were observed. The influence of peening temperature on the distribution of compressive residual stress was analyzed. An optical microscope (OM) and a transmission electron microscope (TEM) were employed to observe the microstructure evolution of the samples before and after LP. The results indicate that, as the peening temperature increases, the micro-hardness increases first and then decreases. The LP process induces high-amplitude compressive residual stress on the surface at different temperatures even if the compressive residual stress slightly reduces with increases in temperature. The maximum compressive residual stress affected layer depth is about 0.67 mm, appearing at a temperature of 160 • C. The OM test revealed that the grain size was significantly decreased after warm laser peening (WLP) and that the average value of grain size was reduced by 50%. The TEM test shows that more dislocation tangles were produced in AA 6061-T6 after WLP; compared to the LP process, the precipitate-dislocation interaction can benefit both strength and ductility for AA 6061-T6, thus enhancing the mechanical properties of the material.

The New Technologies Developed from Laser Shock Processing

“…For instance, the residual stress relaxation in the first 10 cycles (as shown in Figure 12a), and the residual stress at 10 cycles of samples treated by LSP or WLSP at the temperatures of 20, 100, 200, 300 and 400 • C are 16, 42, −19, −86 and −49 MPa, respectively. This similar phenomenon can be also found by the studies of Ye [62] and Huang [65]. So, there exist the most suitable WLSP temperatures to obtain the best stability of residual stress and the highest compressive residual stress.…”

Laser Shock Processing on Metal

“…Microstructural TEM and optical microscopy (OM) analysis reveal a higher dislocation density and more pronounced grain refinement when LSP is performed at elevated temperature. Many dislocations tangled to strengthening precipitates are also shown, which are assumed by Huang et al [4] to be beneficial for improving residual stress stability. This last aspect was confirmed for a similar WLP procedure by Chen et al [5], considering an A356 (Al7Si0.3Mg) cast aluminum alloy.…”

“…The following fields are covered in the seven selected papers: materials' behavior and phase transformations under high strain rate (Amadou et al [1]), new loading conditions with ultra-short pulses (Petronic et al [2]) surface modifications induced by laser peening including recrystallization effects (Zhou et al [3]) and warm laser peening (Huang et al [4], Chen et al [5]), and novel applications of LSP such as water droplet erosion resistance (Gujba et al [6]) or impact spot welding (Liu et al [7]). The wide variety of topics related to LSP highlights the extraordinary dynamism and enthusiasm of the growing international LSP community.…”

Fracture Toughness Prediction under Compressive Residual Stress by Using a Stress-Distribution T-Scaling Method

“…Some examples of such preloading types are warm prestressing (WPS) [1][2][3][4][5][6][7][8][9][10], shot peening, and more recently, laser peening [11][12][13]. One of the common contributors to the benefits of these preloads is CRS, introduced at the crack tip.…”