Effects of Filler Chemical Composition on the Postweld Heat Treatability of Extruded AA7005 Aluminum Alloy

• Main Authors: Kuang-ming Lin, 林昆民
• Other Authors: YE-EE Wu
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/80985386248508841463

碩士 === 國立臺灣科技大學 === 機械工程系 === 93 === Proper fillers selection and postweld heat-treatment can strongly affect the mechanical and stress corrosion cracking (SCC) properties of the weldments of 7000 series aluminum alloy. ER5183, ER5356 and ER5556 having similar chemical compositions are the three fillers commonly used for AA7005 welding process. The objective of this study is to investigate the influence of alloying elements on the postweld heat-treatment process and to select suitable postweld heat-treatment processes for AA7005 aluminum alloy. Postweld heat-treatment processes, such as nature aging, T6 temper, T73 temper and RRA treatment, will be performed. Optical metallographic, micro-hardness test, tensile test, EPMA, SEM, TEM, DSC and SCC test will be conducted to characterize the mechanical and stress corrosion properties of these heat-heated weldments. Experimental results showed that diffusion barriers are presented between the weld metal and HAZ fell on ER5556, ER5183 and ER5556 weldments. The diffusion barrier fell away after solution treatment on ER5356 weldments ,but the same situation did not happened on ER5183 and ER5556 weldments; because this barrier, Zn and Mg could not diffuse between the weld metal and HAZ ,in which the precipitates η’(MgZn2 )which are not extremely fine and distributed inside the grains on the weld metal , and the high content of Mg and Mn which are caused to form Mg2Al3,MnAl6 and(MgMn)3Al10 on the welding process or solution treatment on weld metal; these precipitates cause large particles barriers to the mechanical properties on ER5183 and ER5556 weldments. The strength of AA7005 weldments with ER5356 filler may largely increases after RRA heat-treatment. It can be concluded that T73 heat treatment is the most suitable postweld heat-treatment process for AA7005 aluminum alloy comparing with the other treatment processes.