新SIMA法制备AZ91D半固态坯

利用等径道角挤压试验、半固态等温处理试验、金相显微镜、SEM等试验方法和分析设备，对经过等径道角挤压的AZ91D镁合金在等温处理过程中的微观组织演变进行了研究。通过研究，提出了新SIMA制备AZ91D镁合金半固态坯方法。新SIMA法制备的半固态坯料的微观组织均匀，晶粒球化程度好，晶粒细小，平均晶粒尺寸在20—50μm之间。随着保温时间的延长，新SIMA法制备半固态坯料的微观组织有长大的现象，其可用Ostwald熟化理论描述。随着等温处理温度的升高，晶粒的尺寸先增加后减小，形状系数接近1。随着材料在ECAE中获得的等效应变的增加，半固态坯料的晶粒尺寸减小。     

镁合金ZK60-RE半固态坯的微观组织演变

采用常规铸造法和等径道角挤压分别制备了镁合金ZK60-RE半固态坯;用金相显微镜研究了2种半固态坯料在等温热处理过程中的微观组织演变。结果表明：与传统铸造方法制备的半固态坯相比,采用等径道角挤压制备的半固态坯的晶粒细小、圆整,适合于半固态成形。在等温热处理过程中,2种坯料晶粒粗化的机制是合并长大和Ostwald长大。铸态坯料晶粒液相来源于非平衡凝固时在晶内产生的共晶组织,以及在随后的合并长大过程中晶粒所包裹的液相。随着保温时间的延长,铸态坯料的晶粒尺寸变化情况是：增大、减小然后又增大;而挤压态坯料的晶粒尺寸呈单一增大趋势。     

A356.2合金半固态坯料的复合制备工艺

通过近液相线浇注、等径角挤压和半固态保温处理复合工艺制备了A356.2合金半固态坯料。利用金相显微镜和金相分析系统测量各工艺参数下制得半固态坯料的等积圆直径和形状系数,并对测量结果进行分析。结果表明,该复合工艺可以制备性能优良的A356.2合金半固态坯料,平均晶粒尺寸在57.4～87.2μm之间,形状系数在0.74～0.91之间;近液相线浇注可以获得呈蔷薇状和团状的晶粒细小坯料,等径角挤压使晶粒发生了明显的变形和破碎,累积了大的变形能,保温处理过程中晶粒逐步向近球状和球状转变,同时晶粒尺寸增大。     

挤压件尺寸对等径角挤压成形工艺的影响

为了通过大塑性变形技术制备出满足工业需求的大尺寸块体超细晶材料,采用有限元法模拟了不同尺寸挤压件的1、2道次等径角挤压过程,得到了各挤压件的等效应变、等效应力和载荷曲线.分析得出:挤压件尺寸对等效应变的大小和分布以及等效应力的大小影响甚微;但随着挤压件尺寸的增大,等效应力和2道次等效应变的分布均匀性降低,挤压载荷增大.这表明:经过多道次等径角挤压的大尺寸挤压件可以获得晶粒分布均匀的大块体超细晶材料.     

新SIMA法制备AZ91D镁合金半固态坯

借助于等径道角挤压试验、镦粗试验、半固态等温处理等试验方法,并利用金相显微镜、SEM等试验分析设备,对原始铸坯、镦粗和等径道角挤压3种加工状态的AZ91D镁合金在等温处理过程中的微观组织演变进行了研究.通过与原始铸坯直接等温处理和镦粗后等温处理生成的半固态坯的微观组织作比较,提出了新SIMA制备AZ91D镁合金半固态坯方法.新SIMA法制备的半固态坯料的微观组织均匀,晶粒球化程度好,晶粒细小,平均晶粒尺寸在20～50 μm之间.随着保温时间的延长,新SIMA法制备半固态坯料的微观组织有长大的现象,其可用Ostwald熟化理论描述.随着等温处理温度的升高,晶粒的尺寸先增加后减小,形状系数接近1.随着材料在ECAE中获得的等效应变的增加,半固态坯料的晶粒尺寸减小.     

工艺路线对等径角挤压变形均匀性的影响

等径角挤压被认为是制备块体超细晶材料最有前景的工艺方法之一.采用刚塑性有限元法分析了不同路线多道次等径角挤压后的等效应变分布.结果表明:一道次等径角挤压后坯料中间主要变形区下部坯料的等效应变较低.A路线多道次挤压后,变形更加不均匀,上下表面的等效应变差值增大;C路线挤压后等效应变分布呈上下表面小,中间较高的分布特征,且随挤压次数的增加,中心和上下表面的等效应变差异增大.B_c路线多次挤压后的等效应变分布较均匀,等效应变较高的区域应变相差较小且所占区域较大.模拟结果对于等径角挤压工艺的制定可起到指导作用.     

Al-Mg-Mn合金不等径角挤压有限元分析及实验研究

利用Deform-3D软件对Al-Mg-Mn合金进行了不等径角挤压有限元分析,研究了变形过程中试样的等效应变、等效应力分布规律以及挤压载荷的变化情况,并与同等条件下的等径角挤压进行了对比。模拟结果表明,不等径角挤压过程中,坯料在转角处会同时发生剪切变形与径向挤压变形,所需的挤压力较等径角挤压更大,但单道次应变量显著提升,提高了挤压效率与晶粒细化能力;不等径角挤压后,应变沿坯料长度方向呈现分段分布,从料头区域至料尾方向逐渐增大,然而坯料横截面上各处应变差别较小、无应变层化现象。实验验证结果表明,UECAP工艺可以显著细化Al-Mg6-Mn0.7合金晶粒,与模拟结果相符。     

等径道角挤压预变形AZ61镁合金在半固态等温处理中的微观组织演变(英文)

利用金相显微镜和图像分析设备对等径道角挤压预变形AZ61镁合金在半固态等温处理中的微观组织演变进行研究。先利用等径道角挤压对AZ61镁合金铸坯在310℃进行应变诱导,然后将其在半固态进行不同时间的等温处理。研究结果表明:挤压道次、等温处理温度和变形路径影响预变形AZ61镁合金在半固态等温处理中的微观组织演变过程。在将等温处理温度从530℃升高至560℃的过程中,合金的平均晶粒尺寸从22μm增大到35μm。当等温处理温度为575℃时,平均晶粒尺寸减小。当等径道角挤压的变形路径为BC时,预变形AZ61镁合金在半固态等温处理中获得的微观组织晶粒尺寸最小。     

锐角模具通道等径角挤压有限元分析

采用有限元模拟研究了1100Al锐角模具通道(φ=60°)等径角挤压时的坯料流动、等效应变、挤压应力以及速度分布.与φ=90°模具等径角挤压坯料相比,锐角模具通道等径角挤压可以在坯料内产生更大的等效应变,有助于提高挤压的效率;但挤压过程中在两通道相交外侧尖角处出现死区,由于死区的影响,坯料横截面上等效应变分布不均匀,挤出坯料下表面区域等效应变明显高于其他区域,同时,由于挤压应力明显上升,对挤压设备以及工模具提出更高的要求.因此,锐角模具通道等径角挤压比较适合于塑性较好、强度较低的材料.     

Mg-Al系镁合金半固态坯料制备及触变挤压研究

采用拉伸试验机、金相显微镜和等径道角挤压等试验方法对Mg-Al系镁合金半固态坯料制备及触变挤压过程进行了研究.结果表明,等径道角挤压工艺对Mg-Al系镁合金有很好的应变诱导效果.经过等径道角挤压的Mg-Al系镁合金力学性能高,晶粒细小.等径道角挤压+等温处理方法制备的Mg-Al系镁合金半固态坯的微观组织晶粒细小,球化程度高,微观组织非常均匀.生产的AZ61、AZ80、AZ91D和AM60镁合金角框零件的微观组织细小,抗拉强度分别达到306.8、308.3、299.8、321.6MPa.伸长率分别达到21.6%、28.4%、14.6%和29.6%.     

Preparation of AZ91D magnesium alloy semi-solid billet by new strain induced melt activated method

1 Introduction AZ91D magnesium alloy has received more attention due to its high specific strength, specific rigidity and good dimensional stability and so on[1]. Thixoforming is one of the best methods with regard to forming AZ91D magnesium alloy compone…     

Preparation of semi-solid billet of magnesium alloy and its thixoforming

Preparation of semi-solid billet of magnesium alloy and thixoforming was investigated by applying equal channel angularextrusion to magnesium alloy.The results show that mechanical properties of AZ91D alloy at room temperature,such as yieldstrength(YS),ultimate tensile strength(UTS)and elongation,are enhanced greatly by four-pass equal channel angularextrusion(ECAE)at 573 K and microstructure of AZ91D alloy is refined to the average grain size of 20μm.Through using ECAE asstrain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment,semi-solid billet with finespheroidal grains of 25μm can be prepared successfully.Compared with common SIMA,thixoformed satellite angle framecomponents using semi-solid billet prepared by new SIMA have higher mechanical properties at room temperature and hightemperature of 373 K.     

Reheating microstructure of refined AZ91D magnesium alloy in semi-solid state

By means of equal channel angular extrusion (ECAE) test, upsetting test and metalloseope, reheating mierostruetures of raw casting ingots, materials prepared by SIMA and materials extruded by ECAE in semi-solid state were investigated. The results show that compared with those of raw casting ingots and materials prepared by SIMA, reheating microstrueture of materials extruded by ECAE is the best and the final grain size is the finest. With increasing holding time, a growing phenomenon occurs in reheating microstrueture of materials extruded by ECAE, which can be described by Ostwald ripening law. The average grain size increases firstly, subsequently decreases and the shape factor of grains approaches to 1 as the reheating temperature increases. With increasing equivalent strain, the average grain size decreases. This demonstrates that reheating material extruded by ECAE technology is a good method to prepare AZ91D magnesium alloy semi-solid billets.     

Al2O3sf/AZ91D-Y镁基复合材料二次重熔及等温压缩研究

为了推动半固态加工在镁基复合材料成形中的应用,采用液态浸渗法制备出体积分数为10%的Al2O3sf/AZ91D-Y镁基复合材料,并采用等径道角挤压对镁基复合材料进行了形变诱导。再对镁基复合材料进行了二次重熔,并采用等温压缩实验对镁基复合材料在半固态下的力学性能进行了研究。研究表明：在550℃和560℃时延长保温时间有利于组织的球化,在560℃比550℃时,更加能促进晶粒的结晶球化;在相同的应变速率下,压缩变形时的峰值应力随着加热温度升高而降低;在相同的加热温度下,应变速率越大,峰值应力越大。     

触变模锻成形工艺对镁合金成形件力学性能的影响

采用半固态等温热处理法、近液相线模锻法和等通道角挤压法制备AZ91D—Y镁合金半固态坯料。分别将3种状态的坯料加热到半固态温度区间进行二次重熔后,进行了触变模锻成形。结果表明,在半固态温度为560℃,模锻压力为200MPa的条件下,半固态等温热处理法、近液相线模锻法和等通道角挤压法制备坯料分别保温30,20,15min后触变模锻获得最佳力学性能;随着坯料加热温度的升高,触变模锻成形件力学性能呈现先上升后下降的趋势;增加成形压力有利于触变模锻成形件力学性能的提高;在相同成形条件下,等通道角挤压法制备坯料触变模锻后的力学性能最好,近液相线模锻法次之,半固态等温热处理法较差。     

Severe plastic deformation of commercially pure aluminum using novel equal channel angular expansion extrusion with spherical cavity

Equal channel angular expansion extrusion with spherical cavity (ECAEE-SC) was introduced as a novel severe plastic deformation (SPD) technique, which is capable of imposing large plastic strain and intrinsic back-pressure on the processed billet. The plastic deformation behaviors of commercially pure aluminum during ECAEE-SC process were investigated using finite element analysis DEFORM-3D simulation software. The material flow, the load history, the distribution of effective strain and mean stress in the billet were analyzed in comparison with conventional equal channel angular extrusion (ECAE) process. In addition, single-pass ECAEE-SC was experimentally conducted on commercially pure aluminum at room temperature for validation, and the evolution of microstructure and microhardness of as-processed material was discussed. It was shown that during the process, the material is in the ideal hydrostatic stress state and the load requirement for ECAEE-SC is much more than that for ECAE. After a single-pass ECAEE-SC, an average strain of 3.51 was accumulated in the billet with homogeneous distribution. Moreover, the microstructure was significantly refined and composed of equiaxed ultrafine grains with sub-micron size. Considerable improvement in the average microhardness of aluminum was also found, which was homogenized and increased from HV 36.61 to HV 70.20, denoting 91.75% improvement compared with that of the as-cast billet.     

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion in semi-solid isothermal treatment

1Introduction Thixoforming is one of the best methods regarding manufacture of Mg-Al-Zn alloy components because of its low resistance of deformation compared with solid metal forging and high mechanical properties of formed components compared with liqui…     

AZ91D镁合金等径道角挤压制备半固态坯数值模拟

基于半固态坯采用等径道角挤压（ECAE）制备的应用背景，采用PRO／E建立了等径道角挤压的几何模型，通过压缩实验获取了AZ91D镁合金的高温应力应变曲线，采用有限元软件DEFORM-3D对ECAE挤压变形过程进行了模拟，分析了内外转角部位的应力（平均应力、最大主应力和等效应力）变化、应变分布情况等，以揭示等径道角挤压变形跟模具内转角半径的关系。结果表明，模具内转角半径不为零时，坯料挤压过程中，将有正虚力存在，并且内外转角应力变化不尽相同；应变分布不均匀，具有一定梯度；内转角部位，除了承受剪切，还受到压缩作用，外转角反之。     

螺旋通道长度对纯铝粉末多孔材料等径角挤扭变形的影响

针对等径角挤压和挤扭两种工艺的不足,在充分发挥各自优势的基础上,提出了一种新型的大塑性变形工艺——等径角挤扭(Equal Channel Angular Pressing and Torsion,ECAPT)。采用DEFORM-3D软件对纯铝粉末多孔材料等径角挤扭成形过程进行单道次三维有限元模拟,重点分析螺旋通道长度对变形试样挤压载荷、等效应变、致密行为等场量变化规律的影响。结果表明,相比于传统的ECAP变形,ECAPT工艺螺旋通道的存在,可大大增加变形试样内部的静水压力;合理的螺旋通道长度,可有效提高变形试样的累积应变量和应变分布均匀性,显著改善变形试样的整体致密效果。文章在综合考虑最优数值模拟结果的基础上,自行设计了螺旋通道长度为30mm的ECAPT模具,并进行了相关实验验证,证明了所建立有限元模型的可靠性。