Microstructure and mechanical properties of 2099 Al-Li alloy extrusion materials

The microstructure and mechanical properties of 2099 Al-Li alloy extrusion materials were investigated by optical microscopy(OM),scanning electron microscopy(SEM),ambient temperature tensile testing and fracture toughness testing,and so on.The results show that,when the alloy is aged at T83 heat treatment which includes the first aging treatment(121 ℃,14 h) and the secondary aging treatment(181 ℃,30~66 h),the yield strength improves significantly with the increase of the secondary aging time.The yield strength,tensile strength and elongation are 445 and 491 MPa,543 and 551 MPa and 5.7% and 4.7%,respectively,at the secondary aging time of 48 and 66 h.The elastic modulus is as high as 78.75 GPa and actual density is 2 517 kg/m3.The alloy has superior specific strength and specific stiffness.When the duplex aging is(121 ℃,14 h)+(181 ℃,48 h),the fracture toughness KIC value of alloy is 22.87 MPa m1/2.The crack expands along the microstructure defects,such as the fine recrystallization structure,the coarse insoluble second phase,and so on.