Effect of processing parameters on quench sensitivity of an AA7050 sheet

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2011-01, Vol.528 (3), p.795-802
• Main Authors: Zhang, Xinming, Liu, WenJun, Liu, ShengDan, Zhou, MingZhe
• Format: Article
• Language: English
• Subjects: AA7050 sheet; Al3Zr; Alloying elements; Aluminum base alloys; Applied sciences; Boundaries; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Grain boundaries; Hardening. Tempering; Heat treatment; Homogenization; Homogenizing; Hot rolling; Intermetallic compounds; Materials science; Mechanical properties; Metals. Metallurgy; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitation; Production techniques; Quench sensitivity; Quenching
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2010.07.033

▶ In our work, the influence of heat treatments during processing (homogenization, hot rolling and solution) on quenching sensitivity of an AA7050 sheet have been studied carefully. ▶ Al3Zr particles play a vital role in the quench sensitivity by influence the heterogeneous precipitation sites: the density of the incoherent Al3Zr particles (within recrystallized grains) and the grain boundaries (including sub-grain boundaries) also inducing high quenching sensitivity. ▶ To enhance mechanical properties and obtain lower quench sensitivity, a ramping heat during homogenization, controlled deformation (67% reduction with 3–5s−1 deformation rate) and two-stage solution can lead to a lower recrystallized fraction and more low-angle sub-grain boundaries, decreasing the quench sensitivity of AA7050 sheet with good mechanical properties. Secondary precipitation takes place in alloy 7050 during slow quenching after solution and results in a significantly decreased content of Mg, Zn elements. Optical microscopy, transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD) study showed the distribution of Al3Zr particles plays a vital role in quenching process. The equilibrium η phases mainly precipitate at Al3Zr particles within the recrystallized grains and other high energy areas (primarily grain boundaries). The influence of the processing (homogenization, hot rolling and solution) parameter on the quench sensitivity is also investigated by mechanical property examination (T6 temper). A ramping heat homogenization, controlled hot rolling (67% rolling reduction and 3–5s−1 deformation rate) and two-stage solution treatment result in lesser recrystallization and fewer high angle grain boundaries, and lower the boundary angles within sub-structures. The decreasing number of heterogeneous precipitation sites endows the study alloy with good quenching sensitivity and better mechanical properties.