Ageing Response And Strengthening Mechanism Of Novel Al-Li Alloys

The more trace alloy elements’ addition to the third generation Al-Li ally making the varieties and the morphologies of the precipitates formed during aging more complexes,which make the developing of new alloy with excellent integrated performance more difficult.In this article,the mechanical properties and the microstructures of two kinds of Al-Li alloys at different aged conditions are studied, and the relationships of the alloy composition,the microstructures and the mechanical properties are established.The materials used in this project are 2A97-T4,2A97-T3 and 2060 alloy,and the main contents include the aging response and the strengthening mechanism of the precipitates.Different aged conditions with different microstructres were acquired througth different aging processes.TEM was used to characterize the variety,morphology,number and distribution of the precipitates.TEM and DSC were combined to analyze the aging response;the mechanical properties were achieved through hardness and tensile tests and the age hardening behavior were researched;the strengthening mechanism during aging were analyzed through estabilishing the relationship between the mechanical properties and the microstructres;finally,the effects of alloy elements on the varieties of precipitates,aging response and strengthening mechanism were studied.The characterization of the mechanical properties and microstructures of the aged 2A97-T3 and 2A97-T4 alloy indicates that when aged at 125℃,a reversion was observed in both alloys due to the dissolution of the precipitates.After aged at 125℃/16h+155℃/24 h,the two alloy both had a good combination of yield strength and tensile strength,and the yield strength,tensile strength and the elogation of 2A97-T4 alloy were 497.3MPa、552.7MP and 8.4%.And the yield strength,tensile strength and the elogation of 2A97-T3 alloy were 561MPa、600MPa �'� 8%.The precipates include GP zone,δ’,θ’ and T1,and the precipitation order was GP zone +δ’�'the dissolution of GP zone and δ’�'GP 区+δ’+θ’+a little T1�'δ’+θ’+more T1.The pre-stretch can inhibit the formation of GP zone,accelerate the precipitation of T1,and enhance the strength of the alloy.The study of the mechanical properties and the microstructures of 2060 alloy with different conditions indicated that the mechanical properties kept unchanged overtime after naturally aged 24 h.When aged at 143℃,firstly,the strength enhanced and then changed little.The pre-stretch can accelerate the speed of the aging response.The main precipitates include GP zone,δ’and T1 and the precipitaiton order was as follows:supersaturated solid solution�'GP zone+a little δ’�'a little δ’+a little T1�'δ’+a quantative T1.And the pre-stretch can accelerate the precipitaiton of T1.The comparation of the microsructures and properties of the typical aging conditions of 2A97 and 2060 alloy indicates that the interation of trace Ag and Mg elements can supresse the precipitation of GP zone and θ’,promote the formation of T1.The formation of δ’ has a very close relationship with the content of Li.δ’and θ’can improve the strength and decrease the elogation of the alloy at the same time.The strengthening effect of T1 is greater than δ’and θ’,but T1 will not reduce the plastic obviously.