预热对Al2O3陶瓷激光熔覆层温度梯度影响的模拟

针对铝合金微熔滴沉积成形过程中存在的缺陷问题,沉积制备了7075高强铝合金试样,采用金相显微镜(OM)、扫描电镜(SEM)等分析测试手段对其内部缺陷形貌进行观察,进而研究不同类型缺陷的形成机理.结果表明:铝合金微熔滴沉积成形件内部缺陷主要有孔洞和裂纹.其中孔洞缺陷包括间隙孔洞和凝固收缩孔洞；裂纹包括熔合线裂纹和细微热裂纹,其形成与延展和成形件内部残余热应力集中效应、熔滴重熔效果以及晶粒生长状况等因素有关.在此基础上提出减少或消除各类缺陷的方法,从而促进了该技术在高熔点合金零件制备中的应用.

Numerical Simulation of the Preheating Effect on Temperature Gradient in Laser Cladding Al2O3 Ceramic

High-strength 7075 aluminum alloy samples were fabricated in order to solve the defect problems in the aluminum alloy during metal micro-droplet deposition. The microstructure and defects of the samples were observed by OM and SEM, and the defect formation mechanisms were researched. The results indicate that the main defects of the samples are pores and cracks. The pores include interstitial pores and solidification shrinkage pores. The cracks include the cracking bond lines and the hot cracks, whose formation is related with the concentration of residual thermal stress near the pores, the remelting effect of the droplets and the grain growth. Finally some methods were proposed to reduce or eliminate the defects in the aluminum alloy samples by metal micro-droplet deposition.