Influence of Retrogression Time on Mechanical Properties and Microstructure of 7150 Aluminum Alloy

The influence of the retrogression time on properties and microstructure of 7150-T77 aluminum alloy was studied by hardness testing, tensile property testing, exfoliation corrosion test and TEM. Results indicate that the matrix precipitated eta' phase re-dissolves first, and then phase re precipitates and becomes coarsened with the extending of retrogression time. The ultimate mechanical properties increase first then decrease as retrogression time increases. The critical time of the eta' phase re-dissolution and the eta phase precipitation is 30min, At this point, alloys have the highest ultimate mechanical properties, and the grain boundary precipitatedil eta phase becomes coarsened and discontinuous, leading to lower mechanical properties and better corrosion resistance, peak hardness exists at re aging stage. With the retrogression time extending, the time for the alloy to reach the peak hardness becomes shorter. Optimal T77 aging treatment is 105 degrees C/17h+190 degrees C/30min+120 degrees C/23h. With this treatment, the ultimate tensile strength (sigma(b)), yield strength (sigma(0.2)) and elongation (delta) are 608, 544MPa and 10. 4%, respectively, the exfoliation corrosion test gets EA level, the sigma(b), and delta loss in constant loading tensile testing is 4. 9% and 5. 0%, respectively.