TC4激光拼焊板超塑成形试验研究

Experimental Study on Superplastic Forming of TC4 Laser Tailor-welded Blanks

利用2kW YAG激光机,拼焊了厚度0.93mm细晶Ti6Al4V(TC4)板材,焊缝强度高于母材。焊接熔池区未出现裂纹或大的气孔,焊缝热影响区宽度约为0.3～0.4mm。在温度880℃和应变速率10-3s-1下,模拟分析了TC4激光拼焊板超塑成形过程,获得了压力时间加载曲线。对比研究了TC4激光拼焊板和其母材的超塑成形极限,结果表明:TC4激光拼焊板与TC4母材超塑成形性能无明显差别。微观组织观测显示:随着超塑变形量增大,激光拼焊过程中产生的针状α′马氏体,先转变为板条状马氏体,再因动态再结晶而破碎,同时α+β组织分数逐渐增多。

Fine grained Ti6Al4V alloy sheets with 0.93 mm thickness are tailor-welded using a 2kW Nd:YAG laser machine.At optimal welding parameters,i.e.the combination of laser power,welding speed,focus and shielding argon gas,weld joints without cracks and large porosity were obtained.At room temperature,uniaxial tensile tests were preformed revealing that the strength of weld joints is higher than the parent sheet.At the temperature of 880℃ and the strain rate of 10-3s-1,superplastic forming processes were simulated using a FEM software MSC.MARC and the gas pressure vs.forming time curve was obtained.Superplastic bulging tests of the laser tailor-welded blanks were investigated indicating that the weld joints almost has no negative effect on superplastic deformation.Microstructural observations indicate that the acicular α? martensite produced during welding in the fusion zone transforms into the lath martensite initially and that simultaneous development of the lath martensite fragmentation as a result of dynamic recrystallization and the fraction of(α+?) phase increase as the superplastic strain propagation.