Study on Hot Working, Quenching Sensitivity and Stress Corrosion Cracking Resistance of High Strength Aerospace Aa7000 Series (Al-Zn-Mg-Cu) Alloy

In 1936, Sumitomo Metal Ltd. developed a thin plate called "extra super duralumin" which was resistant to stress corrosion cracking(SCC), and was later used on a zero-type fighter aircraft. This is the first time 7000 series (AlZnMgCu) high-strength aluminum alloy (HS-7000) be practical. Since then, in order to meet the application of aerospace structure and components, 7000 series (AlZnMgCu) alloys with higher specific strength, processability, weldability , and SCC resistance have been developed. However, three problems in the manufacturing and using of high strength aerospace Al alloy of 7000 (HS-7000) series, namely (1) low hot working rate (extrusion speed <0.8mm / s), (2) inability to perform on-line heat treatment; and (3) resistant to stress corrosion cracking(SCC); The Al industry and academia are all hope to overcome these problems. In our pre-research found that the low hot working rate was caused by the lower working temperature than (<450 °C). The alloys will be partially melted at the grain boundary, if the working temperature is greater than 450 ° C, resulting in the fragility and the cracking. The reason for the inable to perform on-line solution treatment is due to the high quenching sensitivity of the alloy. When the alloy has high quenching sensitivity, the alloy will not form a supersaturated solid solution, resulting in a decrease in the strength of the alloy. It is necessary to reduce the quenching sensitivity of the alloy, so that a supersaturated solid solution can be obtained at a lower quenching rate. Therefore, this study attempts to alloy design principles, with a variety of enhanced precipitation heat treatment (such as T6, T76, RRA, etc.), by theoretical to explore these two problems, anti-stress corrosion and achieve development to meet the criteria aerospace materials (AMS) specification.As mentioned above, based on the process of the HS-7000 AlZnMgCu series (especially 7075) alloy, a three-year research plan is planned to investigate: (I)high hot working temperatures causing overheating of the HS-7000 series alloys, (II)Quenching sensitivity, and (III)resistance to stress corrosion, can fully present the practical characteristics of this high-strength aluminum alloy. The3-year plan is:1st year: Effect of alloying and heat treatments on working temperature (ie: solution temperature) of wrought HS-7000 alloys2nd year: Effect of alloying and heat treatments on quenching sensitivity of wrought HS-7000 alloys (ie: resulting in inable to quench on-line)3rd year: Developed a wrought HS-7000 experimental alloy that can be deformed at high speed, on-line quenched, and SCC resistant. Based on the practical value and process troubles of the above- mentioned This study is expected to develop the wrought HS-7000 experimental alloy, which can be used to establish its application information for aluminum academia and industry to provide the valuable references.