Effect of Natural Parking Time on Mechanical Properties of ZL114A Alloy by Low Pressure Casting
The low pressure cast ZL114A aluminum alloy was first treated by solution at(540±5)℃ for 14.5 h and natural aging for different times(1-8 215 h),and then the test alloy naturally parked for 1-100 h was artificially aged at(170±5)℃ for 4 h.The hardness change during natural aging and the effects of parking time on the mechanical properties after artificial aging of the alloy were studied.The results show that the hardness of the alloy basically increased during natural aging,and reached 91.8 HBW after natural aging for 8 215 h,which was lower than 110 HBW after artificial aging.With the extension of parking time,the tensile strength and yield strength of the alloy after artificial aging first increased,and reached peak values of 355.0,303.3 MPa after paking for 10 h,then decreased to the lowest values of 336.7,261.7 MPa after paking for 50 h,respectively,and then increased.The variation of the percentage elongation after fracture of the test alloy was opposite to the strength.In natural parking,due to the low nucleation driving force,the pre-β"phase with low interfacial energy was formed,and then the β"phase with more obvious strengthening effect was formed in the artificial aging process,which was the reason for strength increase after parking within 10 h.The main reason for the subsequent decrease in strength was the redissolution of the unstable solute atomic segregation region(GP region).When the parking time exceeded 50 h,the GP region grew to a stable nucleus size,and the redissolution of the GP region did not occur during artificial aging,resulting in the increase of strength.
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