Effect of Transition Metals on the Tensile Properties of 354 Alloy: Role of Precipitation Hardening

• Published in: International journal of metalcasting 2017-07, Vol.11 (3), p.413-427
• Main Authors: Garza-Elizondo, G. H., Samuel, A. M., Valtierra, S., Samuel, F. H.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Materials Science; Metallic Materials; Structural Materials
• ISSN: 1939-5981; 2163-3193
• DOI: 10.1007/s40962-016-0074-y

The present study was carried out to investigate the effects of minor additions of Ni and Zr, individually or in combination, on the microstructure and tensile properties of 354 casting alloy (Al–9 wt%Si–1.8 wt%Cu–0.5 wt%Mg) at room temperature (25 °C/77 °F) and at high temperatures (155 and 300 °C/311 and 572 °F) using different holding times at testing temperature. An analysis of the data obtained from microstructural and tensile tests shows that the tensile behavior of 354-type cast alloys is strongly influenced by the testing temperature and the holding time at temperature prior to testing. The effect of minor additions of Ni and Zr on the high-temperature performance of these alloys is controlled by their T6-properties at room temperature. The addition of 0.2 wt% Ni and 0.2 wt% Zr improves the T6-tensile properties considerably, compared to the as-cast condition. The addition of 0.4 wt% Ni + 0.4 wt% Zr is not sufficient to resist softening at 300 °C (572 °F)/100 h. The addition of 0.4 wt% Ni to alloy 354 leads to a decrease in the tensile properties, attributed to a Ni–Cu reaction that interferes with the formation of Al 2 Cu strengthening precipitates and affects the age-hardening process. The fine L1 2 (Al 3 (Zr,Ti))-type precipitates is the main feature observed in the microstructure of alloys containing 0.2–0.4 wt% Zr additions. The presence of Q -Al 5 Cu 2 Mg 8 Si 6 phase and Al 3 Ni phase is observed in samples tested at 300 °C (572 °F) after 10 h holding.