The effect of T4 and T6 heat treatments for dynamic impact behavior of casting Mg-Gd-based alloys.

The study of dynamic impact properties of Mg–Gd alloy is important for its application in aerospace, automotive manufacturing and weaponry fields. In this work, the dynamic behaviors of the casting solid-solution (T4) and peak-aged (T6) Mg-6.5Gd-3Y-0.5Zr alloys were investigated at different strain rates by using optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), differential scanning calorimetry(DSC), X-ray diffraction(XRD), transmission electron microscopy(TEM), Vickers hardness testing, and split Hopkinson press bar(SHPB). Due to the dynamic precipitation phase during the SHPB and the residual rare earth hydride(REH) particles produce in the T4 treatment, the compressive strength of the casting T4-sample can reach 485 MPa at a strain rate of 3500 s−1. The casting T6-alloy precipitated a reinforced phase β′ and therefore exhibited an ultra-high compressive strength of 519 MPa at a high strain rate of 4500 s−1. The dynamic compressive strength of a T4 sample is unaffected by strain rates, whereas the dynamic compressive strength of a T6-sample is sensitive. Based on fracture morphology, the cracks are made up of a 45° loading direction crack on the cylindrical surface and a compressed surface crack. The fracture surface is characterized by cleavage planes and dimples. As the deformation strain-rate increases, the number of cleavage planes increases, while the proportion of dimples decreases. Under varied strain rates, it can likewise be deduced that cleavage fracture is the main fracture mechanism of the T6-alloy. • The dynamic compressive strength of T4 sample is not sensitive to strain rates, while that of T6 sample is sensitive. • The dynamic precipitation phases and rare earth hydrides synergistically improve impact resistance of the T4 alloy. • The precipitated reinforcing phase β′ accounts for the ultra-high compressive strength of T6 alloy at high strain rate. [ABSTRACT FROM AUTHOR]