Formation of a Double-Layer Ultrafine Crystal Structure for High-Current Pulsed Electron Beam-Treated Al-20Si-5Mg Alloy

In this paper, the effect of high-current pulsed electron beam (HCPEB) on the microstructure refinement of an Al-20Si-5Mg alloy in the cross-section modified zone was studied, and a double-layer ultrafine crystal structure of the Al-20Si-5Mg alloy was formed. It was found that the cross-section modified zone was divided into three zones, namely, the remelted layer, the heat-affected zone, and the thermal stress wave-affected zone after HCPEB treatment. For the remelted layer, metastable structures were formed due to the rapid heating and cooling rates. For the heat-affected zone, the grain of the aluminum phase was refined due to the cooperative effects of shock wave (formed during an eruption event of the brittle phase), thermal-stress wave (formed during thermal expansion of the alloy surface), and quasi-static thermal stress (formed as a result of an unevenly distributed temperature gradient in the inner material) at high temperatures. For the thermal stress wave-affected zone, the grain refinement was not obvious due to the decreasing energy of the shock wave and the thermal-stress wave at low temperatures. In addition, firm evidence for the tracing of shock waves in the heat-affected zone was demonstrated for the first time and verified for the founding of the broken acicular eutectic silicon. Through this experiment, the mechanical properties of Al-20Si-5Mg alloy materials in both the remelted layer and heat-affected zone were significantly improved after HCPEB treatment.