【作者】 张伟；

【导师】 王洪斌；

【作者基本信息】 辽宁科技大学 ， 材料科学与工程， 2019， 硕士

【摘要】 近些年,6000系铝合金以强度、韧性、耐蚀性等优良的综合性能成为国内外的研究重点。6061合金作为6000系铝合金中的代表,具有热挤压成型性好、强度适中、焊接性能好等优点,已被广泛应用于汽车、高铁、和航空航天等领域。铸轧是一种短流程、低投资、低能耗、高效率的生产工艺,但是铸轧得到6061铝合金板材存在偏析严重、第二相粗大等问题,这大大降低了板材的机械性能。为减少板材成型过程中偏析倾向,细化晶粒尺寸,改善析出相的形貌和分布,改良板材整体性能,本研究中采用了温轧工艺,温轧既可以避免热轧引起的氧化,又可以避免冷轧造成的加工硬化。另外,热处理工艺可进一步消除铸轧和温轧造成的某些缺陷,进而提高综合性能。本文通过OM、SEM、XRD、拉伸试验、硬度测试等手段,主要研究320℃、345℃、370℃和390℃温轧温度和20%、35%、50%、65%、80%压下量对铸轧6061铝合金的微观组织和力学性能的影响,并对温轧板材进行热处理。结果表明:（1）温轧工艺中,当温轧累积压下量达到50%时,6061铝合金铸轧板材中的铸态组织全部转变为轧制组织。合金中第二相随温轧道次的递增逐渐由网格状、片状转变为沿轧制方向的线条状,最终变为细小的颗粒状。（2）铸轧6061合金中主要含有耐热相Al_0.7Fe₃Si_0.3、Al₉Fe_0.84Mn_2.16Si及少量强化相Mg₂Si存在。经过温轧后,产生新的析出相Al_0.5Fe₃Si_0.5。铸轧板材热处理后主要含有耐热相Al_0.7Fe₃Si_0.3、Al_0.5Fe₃Si_0.5以及Al₉Fe_0.84Mn_2.16Si。温轧后热处理,产生新的析出相AlMn_0.75Fe_2.25,同时Mg₂Si相在XRD中没有明显峰出现。（3）6061铝合金铸轧板材温轧时,硬度随压下量的增大呈线性递增,且当温轧温度为370℃时,硬度曲线斜率最大约为2.42。80%累积压下量时,硬度值为84.28 HV,抗拉强度、屈服强度和延伸率分别为209.34 MPa、79.09 MPa和20.11%。（4）温轧6061铝合金铸轧板材（560℃,2 h）固溶后,其DSC曲线与6061铝合金析出峰一样,都由四个放热峰组成。样品经（180℃,8 h）+（210℃,2 h）二级时效后,XRD中无Mg₂Si明显峰。（5）温轧6061铝合金铸轧板材经热处理后,硬度随压下量的增大呈线性递增,且当温轧温度为370℃时,硬度曲线斜率最大为4.9。当370℃累积压下量为80%时,板材硬度达到最大,可达130.8 HV,抗拉强度、屈服强度和延伸率分别为318.76 MPa,88.48 MPa和20.53%。更多还原

【Abstract】 In recent years,6000 series aluminium alloy has become a research hotspot at home and abroad because of its excellent comprehensive properties such as strength,toughness and corrosion resistance.As the representative of 6000 series aluminium alloy,6061 alloy has the advantages of good hot extrusion formability,moderate strength and good weldability,and has been widely used in automobile,high iron,aerospace and other fields.Casting rolling is a short process,low investment,low energy consumption and high efficiency production process,but there are serious segregation and second phase coarseness problems in 6061 aluminum alloy sheet produced by casting rolling,which greatly reduces the mechanical properties of the sheet.In order to reduce the tendency of segregation,refine the grain size,improve the morphology and distribution of precipitates,and improve the overall properties of sheet metal,a warm rolling process is used in this study.The warm rolling can not only avoid the oxidation caused by hot rolling,but also avoid the working hardening caused by cold rolling.In addition,the heat treatment process can further eliminate some defects caused by rolling and rolling,and then improve the comprehensive performance.By means of OM,SEM,XRD,tensile test and hardness test,the effects of warm rolling temperatures at 320℃,345℃,370℃,390℃and 20%,35%,50%,65%and80%reduction on the microstructures and mechanical properties of 6061 aluminium alloy were studied,and the warm rolled sheets were heat treated.The results showed that:（1）In the warm rolling process,when the cumulative reduction reached 50%,the as-cast structure of 6061 aluminium alloy Cast-rolled sheet was transformed into rolling structure.The second phase in the alloy gradually changes from mesh and sheet shape to line shape along the rolling direction with the increase of rolling passes,and finally to fine granular shape.（2）The Cast-rolled 6061 alloy mainly contains heat-resistant phase Al_0.7Fe₃Si_0.3,Al₉Fe_0.84Mn_2.16Si and a small amount of strengthening phase Mg₂Si.After warm rolling,new precipitated phase Al_0.5Fe₃Si_0.5 was formed.The heat-resistant phases Al_0.7Fe₃Si_0.3,Al_0.5Fe₃Si_0.5 and Al₉Fe_0.84Mn_2.16Si are mainly contained in the Cast-rolled sheet after heat treatment.A new precipitated phase AlMn_0.75Fe_2.25 was formed after heat treatment after warm rolling,and Mg₂Si phase had no obvious peak in XRD.（3）The hardness of 6061 aluminium alloy Cast-rolled sheet increases linearly with the increase of reduction,and the maximum slope of hardness curve is 2.4.When the temperature of warm rolling is 370℃.The hardness value is 84.28 HV,the tensile strength,yield strength and elongation are 209.34 MPa,79.09 MPa and 20.11%respectively,at 80%of the cumulative reduction.（4）The DSC curve of hot rolled 6061 aluminium alloy Cast-rolled sheet（560℃,2 h）after solution is the same as that of 6061 aluminium alloy precipitation peak,which consists of four exothermic peaks.There was no obvious peak of Mg₂Si in XRD after secondary ageing（180℃,8 h）+（210℃,2 h）.（5）After heat treatment,the hardness of 6061 aluminium alloy Cast-rolled sheet increases linearly with the increase of reduction,and the maximum slope of hardness curve is 4.9 when the temperature of warm rolling is 370℃.When the accumulative reduction is 80%,the hardness of the sheet reaches the maximum,which can reach130.8 HV.The tensile strength,yield strength and elongation are 318.76 MPa,88.48MPa and 20.53%respectively.更多还原