Hot Tearing Susceptibility of Single-Phase Al-3.8 wt%Zn-1 wt%Mg Alloy Using the Constrained Rod Solidification Experiment: Influence of 1.2 wt%Fe Addition and Grain Refinement

Abstract

The increasing global demand for a substantial lightweighting of automobiles to enable a reduction in the greenhouse gas (GHG) emissions and fuel consumption has led to the adaptation of the high strength Al wrought alloys such as the 2xxx and 7xxx series in near net-shaped manufacturing using the high pressure die casting (HPDC) process. However, the obstacle for this adaptation is the high susceptibility to hot tearing during the solidification of these alloys. A new structural Al alloy for high pressure die casting application was developed from the single-phase Al-Zn-Mg family; a high strength and ductile alloy that could be adapted to manufacturing automotive structural components using HPDC and help with a significant reduction in the overall curb-weight of an automobile and thereby increasing the vehicle fuel efficiency. The objective of this study was to enable a better understanding of the hot tearing phenomenon during solidification of the Al-3.8 wt%Zn-1 wt%Mg alloy, the effect of adding 1.2 wt% Fe to the alloy to improve the castability in HPDC process and the effect of adding Ti as a grain refiner of the primary Al phase during solidification of the alloy using Al-5 wt%Ti-1 wt%B master alloy. The constrained rod solidification (CRS) experiments were carried out to measure transient stress, transient strain, and transient temperature during solidification of the alloy. Improvements to the CRS experiments were also developed to obtain a repeatability of the acquired data. The computerized Tomography (CT) imaging was used to visually characterize the hot tearing. Hypothesis on the factors promoting the hot tearing tendencies in single-phase alloys solidified using net-shaped casting processes has been presented with evidence-based on transient stress-strain and thermal data curves obtained during the solidification experiments.