【作者】 张鹏；

【导师】 罗继相；

【作者基本信息】 武汉理工大学 ， 材料学， 2015， 硕士

【摘要】 汽车轻量化是指在保证汽车综合性能的前提下,尽可能降低自身重量,以实现减重、降耗、环保、安全的目的。据统计,汽车重量降低10%,燃油效率可提高6%~8%,轻量化还有助于汽车操纵的稳定性和冲撞安全性。螺簧座是汽车后桥上用于安装弹簧的支撑件,通常采用的是Q235。为实现汽车的轻量化,本课题选择高强度比的A356.2铝合金材料代替碳钢,采用挤压铸造工艺成型螺簧座,力学性能要求本体取样满足屈服强度220MPa、伸长率4%。在研发铝合金螺簧座的过程中,对挤压铸造技术进行了全面而深入的研究。本实验采用宇部HVSC350PL型挤铸机成型螺簧座,主要研究铸造压力、充型速度以及T6热处理对组织和性能的影响,并结合Anycasting计算机模拟技术,对充型情况和凝固情况进行分析。其中,挤压铸造领域受实验设备的限制而对充型速度的研究很少。在研究过程中,量化实验条件以保证实验的可重复性,如跟踪材料成分、检测含氢量和含渣量以确定熔炼质量等。T6热处理方案为545℃×6h+70℃水淬+180℃×4h,对固溶炉进行温度均匀性实验,并采用分级升温的方法使热处理方案能够准确执行。对螺簧座本体取样进行拉伸实验,并结合计算机模拟结果和SEM、EDS分析,寻找断裂原因并给出进一步提高力学性能的方案。另外,本文还对试验中遇到的问题,如Sr-B的变质效果、孔洞缺陷、热处理气泡、Si偏析等进行研究。研究表明,压力增加凝固时的温度梯度并且促进压力过冷,提高凝固阶段的形核驱动力和降低晶粒的线生长速度,在显微组织中,a-Al相的晶粒度相比于重力铸造明显减小,并且随着铸造压力的增加,晶粒度逐渐减小,不均匀性有所增加,形貌也有团块状的发展趋势,在固溶处理后,共晶相中Si元素析出成团状存在于铝基体中,不同压力下的金相组织趋于一致。随着铸造压力的增加,铸态与T6状态螺簧座的力学性能有较小的增加趋势,但是在一定铸造压力范围内,不建议通过提升压力来提高力学性能。随着充型速度的增加,铸态与T6状态螺簧座的力学性能有明显提高的趋势。较高的充型速度会产生涡流,但是强烈的对流以及冲刷型腔壁也促使产生“游离晶粒”,在一定范围内,可以考虑通过增加充型速度提高力学性能。更多还原

【Abstract】 Automotive lightweighting refers to reduce its weight under the promise of comprehensive performance.It can achieve the purpose of weight loss,consumption reduction,environmental protection and safety.According to the statistics,if vehicle weight is reduced by 10%,fuel efficiency can be increased by 6%~8%.Lightweight also contribute to handling stability and security.Spring seat is supporting part which is used to install the spring on the automobile rear axle,usually is Q235 machined by stamping process.This study select A356.2 alloy instead of Q235,and apply the squeeze casting process.The request of mechanical properties is that yield strength meet the 220 MPa, the elongation meet 4%.In the process of research and development of the aluminum alloy spring seat,the study conduct comprehensive and in-depth research of squeeze casting technology.The experiment apply the ube HVSC350 PL squeeze casting machine to produce spring seat,the influence of foundry pressure,filling velocity and T6 heat treatment on microstructure and mechanical properties are studied,and analyze the filling and solidification situation combining Anycasting computer simulation technology.In the process of research, experimental conditions are quantified to ensure the repeatability of the experiment,such as tracking material composition,detecting slag content and hydrogen content to quantify melting quality.The plan for T6 heat treatment is 545℃x6h+70℃water quenching+180℃+4h,comduct experiment of temperature uniformity of the furance,and adopt hierarchical warming heat treatment to ensure the scheme can be performed accurately.Conducting the stretch experiment,refering to the computer simulation results and the analysis of SEM,EDS,study fracture cause and the scheme of further improvement of the mechanical properties is given.In addition,modification effects of Sr-B,hole defects,bubble of heat treatment,Si segregation were studied.Research shows that the pressure increases solidification temperature gradient and promote the undercooling in pressure,improve nuclear driving force and decrease line growth speed.in the microstructure,size of a-Al phase significantly reduced compared with gravity casting, and with the increase of foundry pressure,the grain size decreases,the nonuniformity increases,ppearance also has the development trend of the crumb.With the increase of foundry pressure,the mechanical properties have a relatively small increase trend,but don’t recommend improve mechanical properties through increase pressure within a certain range of foundary pressure.With the increase of the filling speed,the mechanical properties are improved obviously in state of as-cast and T6.High filling speed produced eddy current, but the strong convection and the scour of cavity wall prompted "free grain".In a certain speed range,mechanical properties can be improved by increasing filling speed.更多还原