A Study on the Factors Enhancing the High-Temperature Strength of B319.2-Type Alloys

The purpose of this study is to investigate the potential of zirconium (Zr) and nickel (Ni) in enhancing the strength of 319-type cast alloys at high temperature. The high-temperature testing was performed on tensile bars either in the as cast or T6 tempered (190 °C/2h) condition. High-temperature tensile tests were performed at 25, 190, 250 and 300 °C. Tensile bars were held at each temperature for 10h prior to pulling to fracture. The results revealed that (Al,Si) 3 (Zr,Ti), Al 3 CuNi, Al 65 Si 16 Ni 13 or ~ Al 4 SiNi and Al 9 NiFe phases are the main features in the microstructures of alloys containing Zr and Ni. In addition, other phases containing Cu such as Al 5 Fe 2 Cu 2 , AlSiFeNiZrCu (probably Al 4 SiNi (Cu, Fe, Zr) or Al 4 SiNi with traces of Cu, Fe, Zr), and Q-Al 5 Cu 2 Mg 8 Si 6 could also be formed. All these phases result in depletion in the Cu content and hence reduction in the alloy strength. Both Al 2 Cu and Al 3 Zr are the hardening phases during artificial aging. The tensile properties were plotted as a function of aging temperature and in the form of Q-charts. The fracture behavior of selected samples was examined as well, using FESEM microscopy.