Secondary Phases Present in Spray Formed Al-10.5Zn-2.0Mg-1.5Cu Alloy

Abstract

Al-10.5Zn-2.0Mg-1.5Cu alloy was produced by spray forming (SF) technique. The initial microstructure, particularly secondary phases, present in the as-SFed alloy was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with attached energy dispersive X-ray spectroscopy (EDS). The results indicated that the equiaxed α-Al grains have an average size of about 18-20 μm in diameter. The intergranular phase was identified as MgZn2 by selected area electron diffraction (SAED) pattern, which was also distributed in the grain interior as well as Al2Mg3Zn3. A needle-like Al23Cu(FeCrMn)4 precipitate was detected. The combined analysis of morphology and crystallographic structure suggested that the Al23Cu(FeCrMn)4 grew along its long axis of <001> orientation. The refinement of the intergranular phases occurred, which is probably due to a decreased amount of eutectic liquid phase finally solidifying on a large area of grain boundaries.

Effect of Hot Deformation and Heat Treatment on the Microstructure and Properties of Spray-Formed Al-Zn-Mg-Cu Alloys

“…The spray-forming process is conducted under a protective environment of high-pressure inert gas, which can mitigate the introduction of impurities such as Fe and Si, thereby reducing the presence of impurity phases like the Fe-bearing phase (Al 7 Cu 2 Fe) and Si-containing phase. Moreover, the solubility of alloying elements is enhanced by the rapid solidification in the spray-forming process, consequently minimizing the precipitation of coarse primary phases [92,113]. It is noteworthy that the absence of the S phase (Al 2 CuMg) in spray-formed Al-Zn-Mg-Cu alloys is reported in some studies, while the presence of the S phase in the spray-formed 7055 alloy has been detected by Si and Yang et al [114,115].…”