自然停放时间对低压铸造ZL114A合金力学性能的影响

Effect of Natural Parking Time on Mechanical Properties of ZL114A Alloy by Low Pressure Casting

对低压铸造ZL114A铝合金先进行(540±5)℃×14.5 h固溶处理,再进行不同时间(1~8215 h)的自然时效处理,然后对自然停放1~100 h的试验合金进行(170±5)℃×4 h人工时效处理,研究了自然时效过程中合金硬度的变化以及停放时间对人工时效后合金力学性能的影响规律。结果表明:在自然时效过程中,试验合金的硬度整体呈增大趋势,时效8215 h时达到91.8 HBW,低于人工时效的110 HBW。随着停放时间的延长,人工时效后试验合金的抗拉强度和屈服强度先升高,在停放10 h时达到峰值,分别为355.0,303.3 MPa,随后降低,在停放50 h时降至最低值,分别为336.7,261.7 MPa,随后又有所升高。断后伸长率的变化规律与强度的变化规律相反。在自然停放过程中由于形核驱动力低,试验合金中形成界面能较低的pre-β″相,在人工时效过程中形成强化效果更为明显的β″相,这是强度在停放10 h内升高的原因;而后强度降低的主要原因为不稳定溶质原子偏聚区(GP区)在人工时效时发生了重溶;当停放时间超过50 h后,GP区长大到了稳定的晶核尺寸,在人工时效处理时不会发生重溶,强度回升。

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(1-8215 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 8215 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 theβ″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.