Al-Mg-Si合金搅拌摩擦焊接头DSC测试过程中组织变化及能量释放分析

MICROSTRUCTURE CHANGE AND ENERGY RELEASE OF FRICTION STIR WELDED Al-Mg-Si ALLOY DURING DSC TEST

对Al-Mg-Si合金搅拌摩擦焊焊核区组织进行了差热扫描量热分析(DSC),同时运用EBSD和TEM观察了焊核区的微观组织,并对存储能进行了定量分析.研究表明,焊核区为不稳定组织,焊核区组织中小角度晶界占42%,大角度晶界占58%,同时晶粒内部分布有较高密度的位错结构.焊核区含有较高的存储能(8.565 J/g),通过EBSD对焊核区较高存储能进行了定量分析,结果表明,位错存储在晶界和亚晶界的能量为0.0247 J/g,存储在晶粒内部的能量为0.0712 J/g.通过DSC定量分析的能量释放来自于焊核区晶粒内部位错的消失和析出相的析出,其中由析出相析出所造成的能量释放占主导作用,位错存储在晶界和亚晶界的存储能通过DSC加热并未释放.

During friction stir welding, the nugget zone （NZ） underwent severe plastic deformation and high temperature. This process resulted in high density of dislocations and dissolving of the precipitation. In this study, the stored energy of the NZ in friction stir welded A1-Mg-Si joint was quantitatively analyzed by means of differen- tial scanning calorimetry （DSC）. The microstructure of the NZ was investigated by electron back scattering diffrac- tion （EBSD） and transmission electron microscope （TEM）. DSC analysis showed that the energy stored in the NZ was about 8.565 J/g. Microstructure investigation showed that the NZ was composed of low-angle grain boundary （42%） and high-angle grain boundary （58%）. Meanwhile, there were high density dislocations in the NZ. The stored energy was quantitatively analyzed based on EBSD data and dislocation density. The results showed that the stored energy resulting from the grain boundary and dislocations was about 0,0247 J/g and 0.0712 J/g, respectively. These results proved that the precipitation played dominant role in stored energy while the contribution of grain boundary and dislocations are negligible.