Pre-Solidified Grains (PSG) in High-Pressure Die Casting (HPDC) of a (Al, Zn, Mg)-Fe(Ti) Dilute Eutectic Alloy

Pre-solidified grains (PSG) are a critical defect that are rising to importance in the as-cast microstructures of conventional aluminum alloys for high-pressure die casting (HPDC) process. These PSG directly influence the mechanical properties of cast components and lead to premature failure during load-bearing operations. The effects of increasing the amount of pre-solidified grains and the accompanying porosity in HPDC by delaying the shot after pouring have been evaluated using plate castings of a new Al-4.7wt%Zn-0.95wt%Mg-1.15wt%Fe-0.07wt%Ti dilute eutectic casting aluminum (DECA) alloy, which, named Nemalloy HE700™, differs from conventional eutectic casting aluminum (ECA) alloys such as Aural™-2, Aural™-5, Mercalloy™, Silafont®-36, and others. The Zn and Mg additions serve to enlarge the solidification temperature range and remain dissolved in both the liquid and solid phases across the entire regime. Plate castings of 220 × 75 × 2.65 mm3 dimensional volume were fabricated using high vacuum HPDC (HVHPDC) process. To enable the formation of PSG, shot delay intervals were deliberately introduced in intervals of 3 s from normal operation conditions of a 1 s delay to a total of 10 s. For each condition, quantitative metallography and uniaxial tensile testing were carried out. The results show that as delay intervals increased, the area fraction of both pre-solidified grains and gas porosity levels both increased. Moreover, the delay in the casting injection shots resulted in the reduction of the ultimate tensile strength and elongation in uniaxial tensile tests.