基于选区激光熔化(SLM)工艺对AlSi7Mg铝合金构件进行激光增材制造实验, 研究了激光能量密度对SLM成形AlSi7Mg构件致密化行为、显微组织, Si析出形态及力学性能的影响规律, 明晰了AlSi7Mg合金SLM成形熔池内温度场和速度场等物理冶金机制, 为激光增材制造AlSi7Mg构件显微组织调控和力学性能提升提供了理论基础。研究表明, 随着激光能量密度由150 J/m增至175 J/m, 激光成形构件的致密度由94.6%提升至近乎全密度(99.6%); 但过高的激光能量输入(225 J/m)则会导致致密度降低至99.0%。过高激光能量密度下, 温度过高的熔池使得部分低熔点合金元素蒸发形成气孔是致密化程度下降的主因。激光增材制造AlSi7Mg构件中Si颗粒呈现良好的弥散分布状态, 且形态十分细小, 呈规则网状分布, 但能量密度过高时Si颗粒会发生粗化, 不利于合金强韧化。在优化的激光能量密度下(200 J/m), 激光增材制造AlSi7Mg构件力学性能获得显著提升, 显微硬度达165 HV, 拉伸强度达475.8 MPa, 延伸率达6.4%, 比传统铸造或粉末冶金AlSi7Mg合金力学性能提高20%以上。

Based on selective laser melting(SLM)process, the AlSi7Mg aluminum alloy parts were produced for laser additive manufacturing experimental study. The influence of laser energy density on the densification behavior, microstructure, Si precipitation morphology and mechanical properties of of SLM-processed AlSi7Mg parts were studied. The physical metallurgical mechanism such as temperature field and velocity field in the molten pool of AlSi7Mg alloy SLM was clarified, which provided a theoretical basis for the microstructure adjustment and mechanical properties of AlSi7Mg parts in laser additive manufacturing. The results showed that as the laser energy density increased from 150 J/m to 175 J/m, the compaction of laser formed parts increased from 94.6% to almost full density 99.6%. However, overlarge laser energy input(225 J/m)led to a decrease of density to 99.0%. Under high laser energy density, the excessively high temperature of the molten pool caused evaporation of part of low melting elements to form gas pores, which was the main reason for the decrease of densification. The Si particles in the laser additive manufacturing AlSi7Mg parts exhibited a good dispersion distribution, and the Si particles were very small and presented a regular net-shape. However, excessive laser energy density led to the coarsening of the Si particles, which was deteriorated the mechanical properties of alloy. Under optimized laser energy density(200 J/m), the mechanical properties of the laser additive manufactured AlSi7Mg parts were improved significantly, with a microhardness of 165HV, an tensile strength of 475.8 MPa, and an elongation rate of 6.4%. Compared to AlSi7Mg alloys fabricated by traditional casting or powder metallurgy, the mechanical properties increased by more than 20%.