激光选区熔化AlSi12合金缺陷产生机制及控制

Mechanism and Control of Defects of AlSi12Alloy Fabricated by Selective Laser Melting

系统研究了工艺参数对激光选区熔化(selective laser melting,SLM)成形AlSi12合金填充及轮廓区缺陷的影响,分析了不同缺陷产生的机理,并提出了控制方法。结果表明,AlSi12合金中未发现裂纹,只有气孔和未熔合孔两类孔洞缺陷。填充区内,随激光功率增大,孔洞由未熔合孔转变为气孔;随扫描间距、扫描速度增大,孔洞由气孔转变为未熔合孔。轮廓区内,当线能量密度过低(0.10 J/mm)时,出现未熔合孔,轮廓与填充区不能良好结合;当线能量密度过高(0.60 J/mm)时,轮廓与填充区结合良好,但出现气孔。未熔合孔产生机制为:粉床输入能量低,液相量少且黏度高,无法良好铺展。气孔产生机制为:粉床输入能量高,金属气化强烈,造成熔池剧烈搅动,卷入的保护气在深熔模式下难以逸出。通过调整工艺参数,控制熔深和熔宽,可在实现良好搭接的同时保证气体逸出,实现填充区及轮廓区均致密成形,致密度达到99.9%,试样性能优良:抗拉强度422.6~446.9 MPa,屈服强度280.4~295.4 MPa,延伸率9.8%~13.0%,显著优于铸造ZL108合金。

The effect of process parameters on the filling and contour defects of SLM AlSi12alloy was studied systematically,and the mechanism of different defects was analyzed,and the controlling method was proposed.The results show that AlSi12 alloy is free from cracks,exhibiting only gas and unfused pores.In the filling area,the pores change from unfused pores to gas pores with the increase of laser power.However,pores changed from gas pores to unfused pores with the increase of the hatch spacing and scanning speed.In the contour area,unfused pores appear when the line energy density is too low(0.10J/mm),and the contour and filling area can not be well combined.The contour and the filling area are well combined when the line energy density is too high(0.60J/mm),but the pores appear.The mechanism of unfused pores is:the input energy of powder bed is low,the liquid phase is less and the viscosity is higher,the liquid can not be well spread.The mechanism of gas pores is:the input energy of powder bed is high,the metal is vaporized strongly and the melting pool is stirred violently,and the involved protective gas is difficult to escape under the keyhole mode.By adjusting the process parameters to control the depth and width of melting pool,the good overlap is achieved and bubble escape is guaranteed.Consequently,the filling area and the contour area are densely fabricated,and the density reaches 99.9%.The mechanical properties are excellent:the ultimate tensile strength,yield strength and elongation of AlSi12fabricated by optimal process parameters are 422.6~446.9MPa,280.4~295.4MPa and 9.8~13.0%respectively,which are significantly superior to those of ZL108alloy.