重力铸造Sr变质B356铝合金的热处理工艺优化

摘要

近年来,采用某些铸造工艺使生产薄壁件成为可能,尺寸上已实现金属型铸造技术能实现小于4mm的极限.因为这些铸件的安全边际量减小,有必要研究Al-7Si-Mg合金的T6热处理条件,以获得最佳的强度和延性组合.此外,必须优化与T6处理有关的成本和生产时间.采用实验研究优化了重力铸造Sr变质B356铝合金薄壁件的固溶强化和人工时效条件.分别选取530℃和550℃作为固溶处理温度,固溶2～8 h,随后水淬,165℃人工时效2～32 h.获得最佳的综合力学性能的热处理条件是:550℃固溶2h,165℃人工时效28 h.DSC分析表明,β"相在人工时效过程中充分析出后,合金达到最佳力学性能.%In recent years,certain foundry processes have made it possible to obtain products with very thin parts,below the 4 mm threshold of the permanent mold casting technology.The safety margins of these castings have been reduced,so the T6 heat treatment conditions adopted for the Al-7Si-Mg alloys need to be investigated to identify the best combination of strength and ductility.Furthermore,the cost and the production time associated with T6 heat treatment have to be optimized.In the present work,an experimental study was carried out to optimize the solution treatment and artificial aging conditions in gravity cast thin bars of B356 aluminum alloy modified with Sr.Two solution temperatures were selected,530 ℃ and 550 ℃,respectively,with solution time ranging from 2 to 8 h,followed by water quenching and artificial aging at 165 ℃ with aging time from 2 to 32 h.The results of hardness and tensile tests were correlated with differential scanning calorimetry (DSC) analysis.The best combination of mechanical properties and heat treatment duration was obtained with 2 h solutionizing at 550 ℃ and 8 h aging at 165 ℃.DSC analysis showed that the alloy's mechanical properties reach the maximum value when the β" phase is completely developed during the artificial aging.