Effect of Retrogression Heat Treatment Time on Microstructure and Mechanical Properties of AA7010
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The effect of retrogression time during retrogression and re-aging (RRA) treatment of AA7010 is evaluated by performing tensile tests and characterizing the microchemistry of the grain boundary precipitates (GBPs) using transmission electron microscope coupled with the energy-dispersive spectroscopy. Retrogression time is evaluated so that the ultimate tensile strength of the RRA-treated sample is equal to that of the T6-treated sample and the grain boundary microstructure similar to that of the over-aged (T7451) condition. The investigation reveals that the sample retrogressed at 200 °C for 20 min has UTS of 586 MPa which is equivalent to that of the T6 sample and 11.5% higher than that of the T7451 condition. The fracture toughness of the RRA-treated sample was 41 MPa√m. Microstructure of the RRA-treated sample is similar to T7451, along the grain boundaries and in the grain interior similar to that of the T6-treated sample. Energy-dispersive spectroscopy confirmed the increment of Cu content on the GBP’s with increase in the retrogression time, which is expected to improve the stress corrosion cracking resistance of the alloy.
Keywordsfracture toughness GBP peak aging RRA SCC TEM
Authors are thankful to The Director, NITK, and The Director, CSIR-NAL, for facilitating to conduct this research work and also for their continuous encouragement. One of the authors Mr. Nandana would like to thank the MHRD-Government of India for providing the scholarship grant. The technical staff at the Department of Metallurgical and Materials Engineering, NITK, is thanked for their support.
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