连续激光冲击强化Al7050中厚板的过喷效应

An over peening effect of Al7050 mid-thick plates with continued multiple laser shock peening at the same positions

摘要:

本文基于连续激光冲击强化7050铝合金中厚板的表面完整性和内部层裂，提出了一种激光冲击强化的过喷效应。7050铝合金中厚板尺寸为50 mm × 50 mm × 5 mm （长×宽×高）。激光工艺参数为激光能量30J，光斑尺寸4 mm × 4 mm，脉宽15ns和单点连续多次激光冲击（LSP-1~LSP-8）。表面形貌，表面残余应力，深度方向显微硬度和截面微观组织分别被超景深三维形貌仪，X射线衍射仪，显微硬度仪和金相显微镜测试分析。研究结果表明：单点连续5次激光冲击诱导7050铝合金中厚板表面微凹坑凸起高度为197.8 μm和山脊高度为130.8 μm。从单点连续4次激光冲击到单点连续5次激光冲击，试样表面残余应力由压应力转换为拉应力。单点连续5次激光冲击后，试样背层产生了低显微硬度的加工软化现象。单点连续5次激光冲击为7050铝合金中厚板的层裂阈值。研究结果有益于激光冲击强化工业应用中避免层裂和改善强化效果。

关键词:7050铝合金中厚板; 激光冲击强化; 过喷效应; 表面完整性;内部层裂

Abstract:

In this paper, an over peening effect was presented based on the researches of surface integrity and internal spall of Al7050 mid-thick plates with continued multiple laser shock peening (LSP) at the same positions. The dimensions of the samples were 50 mm × 50 mm × 5 mm (Length × Width × Thickness). Laser process parameters were laser energy of 30 J, square spots of 4 mm × 4 mm, pulse width of 15 ns and continued multiple LSP at the same positions (LSP-1~LSP-8). Surface morphology, surface residual stress, and micro-hardness in depth and cross-sectional microstructure were measured by Super depth 3D microscope system, X-ray diffraction instrument, Vickers indenter and Optical Microscope (OM), respectively. The results indicated that high micro-dent depressions of 197.8 μm and ridges of 130.8 μm were generated after continued LSP-5. Surface compressive residual stress changed into tensile residual stress from continued LSP-4 to continued LSP-5. After continued LSP-5, work soft with low micro-hardness was found in the bottom layer. Continued LSP-5 was the spall threshold of Al7050 mid-thick plates. The researched results can be beneficial to avoid the spall and improve the strengthening effect in an industry application of LSP.

Key words:Al7050 mid-thick plates; Laser shock peening (LSP); Over peening effect; Surface integrity; Internal spall