热处理对ZL205A残余应力和微观组织的影响

Effect of Heat Treatment on Residual Stress and Microstructure of ZL205A Alloy

结合低压铸造和热处理过程的数值模拟和相关试验,研究了T2和T5热处理对ZL205A铸件残余应力、微观晶粒和析出相的影响。结果表明:热处理前,晶粒为不规则椭圆状等轴晶,枝晶间距在55μm左右,平均晶粒尺寸在60μm左右;组织中存在θ(Al_(2)Cu)相、T(Al_(12)CuMn_(2))相、AlB_(2)相和Al_(3)Ti相、树枝晶状偏析缺陷;铸件残余应力分布不均,存在偏析缺陷的区域残余应力较大;晶粒越致密均匀,残余应力越低。热处理后,铸件发生变形、回复和再结晶,但晶粒只部分破碎,大晶粒吞并小晶粒,晶粒粗化;晶界处共晶组织和偏析缺陷消失,AlB_(2)和Al_(3)Ti相溶解,T相和θ'等强化相析出,呈弥散分布;由于局部塑性变形,残余应力松弛,峰值从200MPa降至138.1MPa,且局部塑性变形越大,残余应力释放越明显。

The effects of T2 and T5 heat treatments on the residual stresses,microscopic grains and precipitate phases of ZL205A castings were investigated by numerical simulations and relevant experiments during lowpressure casting and heat treatment processes.Current findings demonstrated that before heat treatment,the microscopic grains were irregular elliptical equiaxed crystals with a dendritic spacing of about 55μm and an average grain size of about 60μm.Meanwhile,there wereθ(Al_(2)Cu),T(Al_(12)CuMn_(2)),AIB,and Al_(3)Ti phases,as well as dendritic segregation defects in the microstructure.Moreover,the residual stresses were larger in the area with dendritic segregation,the denser and more homogeneous the grains,the lower the residual stresses.After heat treatment,the casting deformation,recovery and recrystallization occurred,but the grains were only partially broken,the grain coarsening as a result of large grains engulf small grains.Meanwhile,the eutectic structure and dendritic segregation at the grain boundaries disappeared,the AlB_(2)and Al_(3)Ti phases dissolved,the T phase and the reinforcing phases such asθ"precipitate in diffuse distribution.Moreover,the residual stresses were released due to the local plastic deformation with the peak value decreased from 200 MPa to 138.1 MPa.The greater the local plastic deformation,the more obvious the residual stress released.