Evolution of A201 alloys microstructure during thermal treatment: influence of Si, Ti and B

19^th World Congress on Materials Science and Engineering

June 11-13, 2018 | Barcelona, Spain

S. Abd El Majid, M. Bamberger, A. Katsman

Technion � Israel Institute of Technology, Israel

Posters & Accepted Abstracts: J Material Sci Eng

Abstract :

Different metastable phases formed during thermal treatment of Al-Cu alloys were investigated by combination of HRTEM, TEM+EDS and HRSEM techniques. The based Al - 4.97 wt. % Cu - 0.56 wt. % Ag alloy (A201) was modified by different additions of Si, Ti and B. Microstructure and mechanical properties were studied in the as-cast, solution treated (at 550��C for ~20 hours) and aged (at 170��C up to 32 days) conditions. The precipitation sequence during aging was the following: supersaturated solid solution (SSSS) â�� GP zones â�� �¸'' â�� �¸' + �© â�� �¸. During the early stages of aging GP zones are nucleated as single layers of Cu parallel to {100} planes of the â��-Al matrix. Then these GP zones are united and generate the metastable �¸''- CuAl3 phase consisting of several single atomic layers of Cu, each of them separated by three atomic layers of Al. The Ag, Ti and B additions resulted in nucleation of metastable semi-coherent �¸ phase formed at {111} �± -Al planes. The Si addition increased nucleation of GP zones and inhibited �© phase. The following aging resulted in �¸" transformation to semi-coherent metastable �¸'- CuAl2. The mechanism of this transformation is discussed. The next step of microstructure evolution is diffusional dissolution of �¸'' precipitates in the presence of more stable �¸' and �© phases. The maximum microhardness corresponded to simultaneous formation of semi-coherent �¸' and �© precipitates. After extended aging, the �¸' transforms to stable incoherent BCT �¸-phase. eng.suzan26@gmail.com