Experimental study on mechanism of influence of laser energy density on surface quality of Ti-6Al-4V alloy in selective laser melting

激光能量密度对选区激光熔化Ti-6Al-4V合金表面质量影响机理的实验研究

This experiment obtained different laser energy density(LED) by changing SLM molding process parameters.The surface morphology, surface quality, and microstructure of as-fabricated samples were studied. The effects of scanning speed, hatching space, and laser power on surface quality were analyzed, and the optimal LED range for surface quality was determined. The results show that pores and spherical particles appear on the sample’s surface when low LED is applied, while there are lamellar structures on the sides of the samples. Cracks appear on the sample’s surface,and the splash phenomenon increases when a high LED is taken. At the same time, a large amount of unmelted powder adhered to the side of the sample. The surface quality is the best when the LED is 150-170 J/mm^(3). The preferred hatch space is currently 0.05-0.09 mm, the laser power is 200-350 W, and the average surface roughness value is(15.1±3) μm.The average surface hardness reaches HV404±HV3, higher than the forging standard range of HV340-HV395.Increasing the LED within the experiment range can increase the surface hardness, yet an excessively high LED will not further increase the surface hardness. The microstructure is composed of needle-like α’-phases with a length of about 20μm, in a crisscross ‘N’ shape, when the LED is low. The β-phase grain boundary is not obvious, and the secondaryphase volume fraction is high;when the LED is high, the α’-phase of the microstructure is in the form of coarse slats, and the secondary-phase is composed of a small amount of secondary α’-phase, the tertiary α’-phase and the fourth α’-phase disappear, and the volume fraction of the secondary-phase becomes low.

通过改变SLM成型工艺参数获得不同的激光能量密度(LED),研究了成形样品的表面形貌、表面质量和微观组织并分析了扫描速度、扫描线间距和激光功率对表面质量的影响,确定了表面质量的最佳LED范围。结果表明,在较低LED时,样品表面出现气孔和球化现象,而样品侧面存在层状结构。在较高LED时,飞溅现象加剧且样品表面出现裂纹,同时大量未熔化的粉末粘附在样品的侧面。LED在150~170 J/mm^(3)范围内得到的表面质量最好。目前优选的扫描线间距为0.05~0.09 mm,激光功率为200~350 W,平均表面粗糙度值为(15.1±3)μm,平均表面硬度达到HV404±HV3,高于锻造标准范围HV340~HV395。在实验范围内增加LED可以增加表面硬度,但过高的LED不会进一步增加表面硬度。试样微观组织主要由长约20μm的针状α’相组成,呈N形。当LED较低时,β相晶界不明显,次生相体积分数较高;当LED较高时,微观组织的α’相呈粗板条状,次生相由少量二次α’相组成,三次α’相和四次α’相消失,次生相体积分数变低。