Observations on the distribution of iron and silicon particles in a high-strength aluminum alloy

Abstract

Iron- and silicon-containing impurity particles have been shown to be detrimental to the mechanical properties of high-strength aluminum alloys. This work studies the relationships between area percent of impurities and stringer spacings in 7×75 (Cr containing) and Zr-modified 7×75 type aluminum plate with five iron and silicon contents and two tempers. Total iron and silicon in the 5 8 -inch-thick plate varied between 0.02 and 0.31 wt%. The commercial T651 temper and a thermomechanical processing (TMP) temper were applied to the plates resulting in 20 combinations of composition and processing. Area percent of impurities varied considerably among the three perpendicular planes of polish in the T651 plates. The TMP plates, with their warm rolling step, exhibited both smaller particle sizes and a more homogeneous distribution of particles. There were more identifiable stringers in the T651 plates than in the TMP plates. An empirical relationship was found to exist between area percent of impurities and stringer spacing in the T651 plates. The TMP plates containing Zr displayed a similar trend; however, the TMP plates containing Cr did not. This difference in behavior was attributed to the fact that the TMP treatment used was developed using a Zr-containing alloy.