【作者】 王小军；

【导师】 丁浩； Tim Sercombe；

【作者基本信息】 中国地质大学（北京） ， 岩石矿物材料学， 2014， 博士

【摘要】 针对传统的铸造铝合金成型中对复杂形状零部件的生产存在模具成本高、生产周期长、材料利用率低等突出问题，本论文研究了选择性激光熔化（SLM）Al-Si合金的工艺参数及力学性能，讨论了工艺参数和热处理工艺对SLM Al-Si合金的显微形貌、物相分布及力学性能的影响，取得一些重要研究成果。获得了SLM Al-Si合金的最优化工艺参数为：激光能量，200W；激光扫描速度，375mm/s至1125mm/s；激光扫描间距，0.15mm；激光停留时间，80μs；铺粉层厚，50μm；保护气氛，Ar或N2。揭示了不同工艺参数条件下选择性激光熔化Al-Si合金的微观形貌、物相分布和力学性能。SLM Al-Si合金的微观结构由纳米级球状Si颗粒和岛状的Al基体组成，部分Si颗粒被固溶到Al基体中形成了固溶强化。本研究制得的不同Si含量的SLM Al-Si合金的强度和韧性均优于铸造Al-Si合金，其中，Al-12Si合金的断裂强度（368MPa）提高了22.7%，屈服强度（224MPa）是铸造性能的1.5倍，断裂韧性（4.8%）也提高了1倍。随着Si含量的增加，SLM Al-Si合金的断裂强度和屈服强度增大，断裂韧性减小。研究了热处理工艺对SLMAl-Si合金微观形貌、力学性能和冲蚀磨损性能的影响，500℃不同时间热处理后SLMAl-Si合金的微观结构中Si颗粒由纳米级长大为微米级，且均匀分布在Al基体中，使得SLM Al-Si合金的强度有所降低，韧性大幅提高，其中Al-12Si合金的断裂韧性（延伸率为25%）提高了5倍以上。180℃不同时间的时效处理后发现SLM Al-10Si-0.35Mg和Al-7Si-0.6Mg合金的屈服强度有大幅提高，分别在12h和24h时达到了最大值为210MPa和227MPa，实现了明显的强化效果。热处理前不同Si含量的SLM Al-Si合金样品的体积冲蚀率均高于热处理后SLM Al-Si合金的体积冲蚀率。SLM Al-Si合金在冲蚀磨损过程中主要发生了塑性变形。对SLM工艺中存在球化、热影响区、裂纹、残余应力等缺陷及形成机理进行分析并得到：激光能量密度过高或过低均会引起球化，通过优化工艺参数可防止球化缺陷的产生；激光的热辐射会导致两相邻激光扫描轨迹之间产生热影响区，造成组织不均匀，影响材料的力学性能，通过适宜的热处理能够有效地消除热影响区；裂纹的产生主要受金属粉体本身性能的影响较大，增加合金的抗热裂性能够有效地防止热裂纹的形成；残余应力和翘曲变形主要是由于熔池上下表面的冷却速度不同造成的，减小熔池上下表面的温度差是减少残余应力和翘曲变形的有效途径。本论文通过对Al-Si合金的SLM工艺及性能的研究，成功制备高性能的Al-Si合金，揭示了工艺参数和热处理工艺对SLMAl-Si合金组织及性能的影响规律，为Al-Si合金的快速成型（3D打印）工业应用和矿物加工用复杂形状流部件制备提供了重要的技术依据和理论基础。更多还原

【Abstract】 Traditional casting fabrication method of Al alloy components requires tooling ordies to shape the parts. These lead highly cast, long production cycle and low materialutilization, especially for small production of complex parts. In this work, theparameters and properties of Selective Lase Melting (SLM) Al-Si alloy were studied.The effect of process parameters and solution treatment on the microstructure, phasedistribution and mechanical properties were discussed. Some important results havebeen obtained.The optimized parameters of SLM Al-Si alloy have been achieved. The laserpower is200W, laser scan speed is375to1125mm/s, exposure time is80μs, laserscan space is0.15mm, laser thickness is50μm, atmosphere is Ar or N2. Themicrostructure of SLM Al-Si alloy is composed by nanometer-sized Si particles andAl matrix as a result of the rapid cooling. And solid solution strengthing was causedby part of Si particles solid soluted in the Al matrix. The SLM Al-Si alloys withdifferent Si content were all superior to those produced by casting method. SLMAl-12Si alloy got1.5times the yield strength,22.7%higher ultimate tensile strengthand twice the elongation to failure. The strength of SLM Al-Si alloys increased asincreasing Si content, while the ductility decreased.The influence of solution treatment on the microstructure and properties wasexplored. After solution treatment at500℃, the fine Si particles have formed asmicron-sized, rounded particles and uniformly distributed in the Al matrix. Thoughthe yield stress and the ultimate tensile strength were reduced a little, there is a largeincrease in the ductility after solution treatment. The ductility of SLM Al-12Si is25%which increased more than5times. The aging treatment at180℃on the SLMAl-10Si-0.35Mg and Al-7Si-0.6Mg shows that Mg2Si phase could significantlyimprove the yield strength of SLM Al-10Si-0.35Mg and Al-7Si-0.6Mg, respectively210MPa and227MPa.The defects and formation mechanism during the SLM were also analyzed anddiscussed. The balling phenomenon is normally caused by the inappropriate laserenergy density. The optimized SLM process parameters of can reduce the formation of balling defect. Laser radiation of two adjacent laser tracks will cause heat-affectedzone, which resulted in disuniform microstructure and damaged the mechanicalproperties of materials. Reasonable heat treatment can effectively promote thediffusion of alloy elements, eliminating the heat-affected zone. Cracking of SLMsamples is caused mainly by the properties of the metal powders. The heat cracking ofSLM alloys could be prevented by increasing the thermal cracking resistance of alloys.Residual stress and deformation is generated mainly by the big difference of coolingrate on the upper and lower surfaces of the molten pool. How to avoid the cooling rateof upper and lower surfaces in the molten pool is an effective way to reduce theresidual stress and deformation.In this paper, the parameters and properties of Selective Lase Melting (SLM)Al-Si alloy were studied. And high performance SLM Al-Si alloys have been obtained.The influence of solution treatment on the microstructure, phase distribution andmechanical properties were also discussed. The results will provide the experimentaldata and theoretical basis for the industry of SLM Al-Si alloy.更多还原