Classification and Evolution of Porous Defects in Spray-Formed Al–Zn–Mg–Cu Alloy

Abstract

The porous defects classification in spray-formed Al–Zn–Mg–Cu alloy was investigated in this paper during spray forming, hot isostatic pressing (HIP) and homogenization. Metallographic microscopy and scanning electron microscopy (SEM) were used to study the microstructure and porous defects. The results showed that, there were four kinds of porous defects in spray-formed alloy, which were distinguish by the reasons of formation and shape. The first kind, the second kind and the third kind porous defects contain gas, while the forth kind porous defect did not contain gas. The forth kind porous defects can be eliminated by HIP, but the other three only can be compressed to be smaller. After homogenization, the porous defects with gas grew up and was observed easily again, unless some porous defects connected with ingot surface through the other porous defects which could exhaust gas during HIP. The second phase in the ingot restored back mostly after the homogenization treatment of 440 °C/12 h + 474 °C/48 h.