Comparative Analysis of Structure and Properties of Nb-B Inoculated Direct Chill Cast AA4032 Alloy Extruded from As-Cast and Homogenized Conditions

Abstract

Al-Si wrought piston alloys can lack properties due to inefficient grain refining. A novel Al-Nb-B grain refiner was introduced some time ago, but has still not been assessed in industry for wrought alloys. This paper describes the first trial of Al-Ni-B addition and its impact on the full-scale manufacturing, structure, and properties of the AA4032 products extruded with and without billet homogenization. It is shown that Nb-B inoculation gives opportunities not only to have a refined as-cast structure but also a more homogenous distribution of the solute. In contrast, homogenization drives nucleation and coarsening of the Mg2Si phase that is retained during further extrusion and heat treatment also affecting the precipitation and properties. It was observed that non-homogenized specimens perform better during machining and tensile testing compared to homogenized specimens. The results are supported by electron microscopy investigations of microstructure formation during different steps in downstream processing.