Research on microscopic strain field of high-pressure die-cast Al7Si0.2Mg alloy under dynamic loading by dislocation-density based crystal plasticity model

• Under dynamic loading at 100 s −1 , the local strain near the porosity was not obvious compared to quasi-static loading, thus significantly lowering the sensitivity of microscopic strain field to porosity. • Under dynamic loading, the mutual coupling between dense second phases and Al matrix further hindered dislocation motion, exacerbating strain localization in the Al–Si alloy. • Eutectic silicon phase with high area fraction and small particle spacing has a significantly stronger impediment effect on dislocations than Fe-rich phase. The microscopic strain field of high-pressure die-cast (HPDC) Al–Si alloy at high strain rate (100 s −1 ) was investigated. A multiscale coupling model based on dislocation-density based crystal plasticity (CP) and representative volume element (RVE) was adopted. By combining electron backscatter diffraction (EBSD) and crystal plasticity modeling, the effects of porosity, grain orientation and second phases on microscopic strain field at different strain rates were systematically explored. The results indicated that multi-slip systems activated at high strain rates generated slip bands, and accumulation of dislocations led to uniform distribution in high-strain regions. This reduced strain concentration near the porosity compared to quasi-static loading, thereby decreasing the sensitivity of porosity to microscopic strain fields. In addition, when densely distributed second phases were present at grain boundaries with large orientation differences, their interaction hindered dislocation motion, resulting in obvious strain concentration along the grain boundaries under dynamic loading. Moreover, due to high area fraction and small spacing of eutectic silicon particles, their obstruction effect on dislocations was higher than that of Fe-rich phase at high strain rate. As a result, eutectic silicon phase contributed more to strain concentration during dynamic deformation.