【作者】 罗江勇；

【导师】 张卫文；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2011， 硕士

【摘要】 Al-Zn-Mg-Cu系合金是一类超高强铝合金,广泛应用于航空航天、交通运输等部门。挤压铸造技术可获得晶粒细小、组织致密、性能高的毛坯或零件,是一种结合了铸造和锻造特点的先进高效近净成形技术。本文采用挤压铸造技术制备了一种(质量百分数)Al-6.5~7.5 Zn-2.0~3.0 Mg- 1.8~2.2 Cu合金(代号HGZL05),采用流动性测试、拉伸性能测试、金相、扫描电镜、差热分析等技术研究了合金的组织和性能。主要结果如下:研究了HGZL05合金在不同挤压力下的显微组织与力学性能,并对比研究了HGZL05合金与一种Al- Si- Cu合金(代号HGZL04)的流动性能。结果表明,浇注温度为720℃和740℃时,HGZL05合金的流动性能要优于HGZL04合金,并且浇注温度越低时,这种优越性更显著;无论是铸态还是热处理态,HGZL05合金的抗拉强度和伸长率均随着挤压力的增大而增大,热处理后,75 MPa下该合金的典型力学性能为:抗拉强度520 MPa,屈服强度405 MPa,伸长率15.8 %,布氏硬度150。当挤压力由0 MPa增大到75 MPa,合金的晶粒尺寸明显减小,由125~130μm减小到65~70μm。研究了杂质Fe含量对合金显微组织和力学性能的影响,并分析了挤压力对Fe相分布和形貌的影响。研究表明,高Fe含量合金的力学性能明显低于低Fe含量合金,但随着挤压力的增大,高铁含量合金和低铁含量合金之间的力学性能的差值逐渐缩小,当挤压力由0 MPa增大到75 MPa时,抗拉强度差值由18 MPa减小到7 MPa,伸长率差值由1.2 %减小到0.4 %;随着挤压力的增大,高Fe含量合金中脆性含Fe相尺寸和分布形态发生了变化,深灰色含Fe相在晶界处呈长条链状聚集分布逐渐变为短杆状离散均匀分布,在Fe相应力集中引起的沿晶断裂处产生了韧性断裂特征。对比研究了挤压力对四种研制合金(HGZL02、HGZL03、HGZL04和HGZL05)的耐腐蚀性能的影响。结果表明,在相同的腐蚀时间下,腐蚀速率由高到低的次序是:HGZL05、HGZL02、HGZL04、HGZL03,四种合金具有不同腐蚀性能主要是由于合金的显微组织和腐蚀形貌不同所致。腐蚀时间一定时,随着挤压力由0 MPa增大到50 MPa,四种合金的腐蚀速率均略有上升,这主要是因为挤压力对合金中晶粒尺寸、第二相形貌及分布产生影响,随着挤压力的增加,四种合金的腐蚀坑尺寸均有所减小,腐蚀坑密度显著增加,腐蚀坑面积所占比例增大,晶间腐蚀深度增加。更多还原

【Abstract】 Al-Zn-Mg-Cu alloys are widely used in aerospace, transportation and other industrial fields due to their super high strength. As a near-net-shape materials processing, squeeze casting that combines the characteristics of casting and forging can produce nearly full dense, fine grain structures. In this paper, the Al-6.5~7.5 Zn-2.0~3.0 Mg-1.8~2.2 Cu alloy named HGZL05 were prepared by squeeze casting. The microstructures and properties of the alloy were studied by fluidity testing, tensile testing, optical microscope, scanning electronic microscope and differential scanning calorimetry. The results are as follows:The effect of applied press on microstructure and mechanical properties of HGZL05 alloy was investigated and the comparative study of the castability of HGZL05 and HGZL04 was also carried out. The results indicate that the fluidity of HGZL05 is superior to HGZL04 when the pouring temperature is either 740℃or 720℃. And the fluidity of HGZL05 shows much better at the lower temperature since the melting temperature of HGZL05 is lower than that of HGZL04. The mechanical properties of both as-cast and heat-treated HGZL05 are improved with the increase of applied press. In condition of the induced pressure of 75MPa, the heat-treated HGZL05 has the tensile strength of 520MPa, yield strength of 405 MPa, elongation of 15.8% and HB of 150. The grain size of the alloy reduces from 125 ~ 130μm to 65 ~ 70μm when the pressure increases from 0 MPa to 75 MPa.The effect of Fe content on the microstrutures and mechanical properties of HGZL05 and the influence of applied press on the distribution and morphologies of Fe phase were studied. The results indicate that the mechanical properties of high Fe content alloy are lower than that of low Fe content alloy. However, the mechanical properties discrepancies of two different Fe content alloys reduce as the squeeze pressure increases. The tensile strength and elongation of the alloy reduce from 18 MPa to 7 MPa and from 1.2 % to 0.4 %, respectively. As the squeeze pressure increases, the size, distribution and morphology of Fe phase change obviously. The accumulated long deep-grey Fe phase changes to dispersive short one, which leads to the ductile fracture around the Fe phase where the intergranular fracture generally occurs caused by stress concentration.The comparative study of corrosion resistance of HGZL02, HGZL03, HGZL04 and HGZL05 alloys were performed. The results show that the order from high to low of corrosion rate of the alloys is HGZL05, HGZL02, HGZL04 and HGZL03 at the same corrosion time. The difference of the corrosion rate is mainly due to the difference in microstructures and corrosion morphology of the alloys. The corrosion rate of the four alloys all increase slightly with the increase of the applied press from 0 MPa to 50 MPa. The reason is that the grain size, morphology and distribution of the second phases are affected by the applied press. As the applied press increases, the grain size reduces and the corrosion area, the depth of intergranular corrosion all increase for the four alloys.更多还原