【摘要】：激光噴丸技術通過激光誘導等離子體產生高幅沖擊波壓力,向材料表層植入高幅殘余壓應力,同時增加表層位錯密度、細化晶粒以提高材料的機械力學性能。針對強化性能在高溫和循環(huán)載荷條件下的穩(wěn)定性問題,溫度輔助的激光噴丸強化技術已日益受到國內外學者的關注。本文以典型航空鋁合金2024-T351為研究對象,探索深冷預處理對2024-T531鋁合金組織性能及激光噴丸強化效果的影響,主要工作包括:(1)理論上探索了深冷預處理對激光噴丸2024-T351鋁合金殘余應力及疲勞性能的影響,分析了激光噴丸誘導殘余應力場、殘余應力對金屬疲勞性能的影響及高溫、振動和交變載荷條件下殘余應力穩(wěn)定性等關鍵問題,研究了深冷預處理對2024-T351鋁合金材料屈服強度、硬度以及彈性模量等力學性能影響的相關理論,為深冷預處理和激光噴丸改性工藝研究提供理論基礎。(2)實驗研究了深冷預處理對2024-T351鋁合金微觀組織、靜態(tài)力學性能及表面殘余應力的影響。以液氮(-196℃)為介質對鋁合金材料進行2h~12h等不同時長的深冷預處理,隨后進行常溫拉伸和納米壓痕等性能測試;對深冷前后材料金相組織、第二相狀態(tài)和表面殘余應力進行檢測分析。結果表明,深冷預處理后材料的微觀組織得到改善,其抗拉極限、屈服強度、納米硬度及彈性模量等明顯提高,拉伸斷口形貌的局部解理特征向塑性斷裂特征轉化,說明深冷預處理亦可提高2024-T351鋁合金塑性。殘余應力測試表明深冷預處理可消除2024-T351鋁合金表面殘余拉應力,并引入小幅殘余壓應力。(3)開展了激光噴丸處理2024-T351鋁合金系列實驗及其相關性能測試,研究了經深冷預處理和未處理材料的激光噴丸強化效果。結果表明深冷預處理后進行激光噴丸處理,材料的晶粒更加圓整且晶界更為清晰,表面殘余應力幅值和激光噴丸影響層硬度明顯增加;“梯度交變載荷”作用下的殘余應力穩(wěn)定性和疲勞性能測試分析表明,深冷預處理和激光噴丸均能提升2024-T351鋁合金的疲勞壽命,同時深冷預處理能顯著提高激光噴丸2024-T351鋁合金殘余應力場的穩(wěn)定性,因而深冷后進行激光噴丸處理的材料疲勞增益更明顯。
[Abstract]:Laser shot peening technique produces high amplitude shock wave pressure by laser-induced plasma, implants high amplitude residual compressive stress into the surface layer of the material, increases the dislocation density of the surface layer, and refines the grain size to improve the mechanical and mechanical properties of the material. Aiming at the stability of strengthening performance under high temperature and cyclic load, the temperature-assisted laser shot peening technique has been paid more and more attention by scholars at home and abroad. In this paper, the effect of cryogenic pretreatment on the microstructure and properties of 2024-T531 aluminum alloy and the effect of laser shot peening on the microstructure of typical aviation aluminum alloy 2024-T351 were studied. The main works are as follows: (1) the effects of cryogenic pretreatment on residual stress and fatigue properties of laser shot peening 2024-T351 aluminum alloy are studied theoretically. The residual stress field induced by laser shot peening, the effect of residual stress on metal fatigue performance and high temperature are analyzed. The influence of cryogenic pretreatment on the yield strength, hardness and elastic modulus of 2024-T351 aluminum alloy was studied. It provides a theoretical basis for the study of cryogenic pretreatment and laser shot peening. (2) the effects of cryogenic pretreatment on microstructure, static mechanical properties and surface residual stress of 2024-T351 aluminum alloy were studied experimentally. Aluminum alloy materials were pretreated with liquid nitrogen (-196 鈩，

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