Iron-rich intermetallics in high pressure die cast A383 aluminum alloys

This work describes the composition and crystal structure of Fe-rich intermetallics that form during the high pressure die casting (HPDC) process of alloy A383. Engine castings were produced using the HPDC process with A383 material with a nominal iron content of 1 wt %. Quantitative energy dispersive X-ray spectroscopy (EDS) was used to measure the chemical composition of Fe-rich intermetallics that formed during the process, and electron backscattered diffraction (EBSD) was used to identify their corresponding crystal structures and space groups. The results revealed that there were two types of Fe-rich intermetallics: sludge particles with a polygonal morphology and alpha-Fe with a Chinese-script shape. No needle-like ss-Fe intermetallics were observed. Sludge and alpha-Fe had the same crystal structures, indexed as body-center cubic (bcc) with the same space group of Im (3) over bar (No. 204). Sludge contained more Mn and Cr than alpha-Fe, whereas there was a larger concentration of Cu in alpha-Fe than sludge. ThermoCalc software was used to estimate the formation temperature of Fe-rich intermetallics, and the results suggested that alpha-Fe (Al8Fe2Si) with the bcc crystal structure and sludge were the same phase but formed at different temperatures during solidification process.