No abstract

No abstract

The grain refinement by dynamic recrystallization (DRX), the enhancement of room-temperature strength and ductility by decreasing hot extrusion temperature, and the effect of grain growth at elevated temperatures are discussed for a newly developed as-cast Mg-Gd-Al-Zn magnesium alloy. The results are supported by fracture surface observations, texture analysis by Schulz reflection method based on X-ray diffraction (XRD), and work-hardening rate plots. It is found that by decreasing the extrusion temperature, the ductility of alloys enhances, which is related to the weakening of basal texture by the rare earth element Gd. Moreover, the grain growth annealing resulted in decreasing the strength and increasing the ductility in the conventional manner, where the texture intensity remained unchanged.

In current research different amounts of La (0.01, 0.03, 0.05, 0.07, 0.1, 0.3, 0.5 and 1 wt%) were added to A357 aluminum alloy to investigate the structure and tensile properties of thin section parts prepared by gravity die-casting. The cast specimens were examined by using optical microscopy (OM), scanning electron microscopy (SEM), tensile testing and determination of quality index values to evaluate the modification efficiency of the alloy by La addition. Obtained results revealed that La reduces the grain size of A357 alloy from 620 µm to minimum 300 µm and improves the morphology of eutectic silicon in as-cast condition. Al 4 La and AlSiLa intermetallic phases were detected through the microstructural studies. The optimum amount of La was found to be 0.1 wt% by enhancing ultimate tensile strength (UTS) of the alloy from 226 MPa to 267 MPa. Further improvement in tensile strength was achieved after T6 heat treatment for 0.1 wt% La added specimens, in which UTS showed the highest value (420 MPa). The addition of 0.1 wt% La also increased El.% values from 3.8 % to 6.8 % in non-heat treated and from 6.2% to 9% in T6 heat treated alloys.

Abstract