Microstructure and properties of AZ80 magnesium alloy prepared by hot extrusion from recycled machined chips

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Hot profile extrusion of AA-6060 aluminum chips

Analyses of energy consumption in manufacturing processes have shown that most of the energy is needed for the production of material such as aluminum or steel and not for further manufacturing steps like forming or cutting. To reduce energy consumption and also a reduction of CO₂ emissions in manufacturing processes, a reduction of the amount of primary material, made from first melting after mining, as well as secondary material, made from melting of recycled scrap material, is needed. In this work, the re-use of aluminum AA-6060 scrap based on milling and turning chips, by direct hot extrusion is presented. To prevent further use of primary aluminum or melting of the chips the process aims at using compacted chips as billet material. The production of the chips as well as the compaction of billets, the extrusion process and the properties of the final profile is presented. In addition to the use of chips based on one alloy the mixture and extrusion of aluminum and SiC particles is presented. The investigations have shown that using billets made of AA-6060 chips can lead to similar mechanical and microstructural properties as using of conventional cast aluminum billets. Investigations on an additional cutting or drilling of the extruded profiles have shown even improved properties due to a reduced chip length.     

Recycling of AZ91 Mg alloy through consolidation of machined chips by extrusion and ECAP

AZ91 Mg alloy recycled by a solid state process and equal channel angular pressing (ECAP) exhibited a superior strength. The mechanical properties of AZ91 Mg alloy recycled from machined chips by extrusion at 623 K and ECAP at 573 K and 623 K were compared with those of the reference alloy which was produced from an as-received AZ91 Mg alloy block under the same conditions as the recycled alloy. The recycled specimens show a higher strength at room temperature than the reference alloy. The improvement of the tensile properties is attributed not only to the small grain size, but also to the dispersed oxide contaminants.     

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%.     

固相再生AZ31B镁合金的组织与力学性能

在不同的挤压温度和挤压比下,将AZ31B镁合金机加屑冷压后热挤压固结而再生镁合金。与铸锭挤压合金对比,从动态再结晶组织与屑间结合情况两个主要方面分析了加工工艺对再生合金力学性能的影响。随着挤压温度升高,再生合金的极限抗拉强度和延伸率先增加而后降低。随挤压温度升高,晶粒长大与屑间结合增强的相反作用共同导致了再生合金力学性能的变化。当挤压比从4:1 增加到 44:1,晶粒细化且屑间结合增强,使再生合金的抗拉强度增加。而当挤压比高于25:1时,由于显著的形变强化作用导致延伸率下降。     

Microstructure and mechanical properties of AZ31B magnesium alloy prepared by solid-state recycling process from chips

AZ31B magnesium alloy chips were recycled by three solid-state recycling processes including cold-pressing, hot-pressing followed by hot extrusion and double extrusion. Microstructure and mechanical properties of the recycled specimens and reference specimens were compared. For the recycled specimen by cold-pressing, the grains are refined to a large extent during hot extrusion due to the presence of twins and high density dislocation. The recycled specimens by hot-pressing and double extrusion do not exhibit finer grain than that the recycled specimen by cold-pressing. Consequently, higher ultimate tensile strength of the recycled specimen by hot-pressing and double extrusion is not achieved. For hot pressing process, more compact billet lowers the porosity in recycled material, so elongation to failure of the recycled specimen increases. The recycled specimen fabricated by double extrusion process shows slightly higher elongation than the reference specimen. The second extrusion makes the oxides further crush and distribute more dispersedly, and minimizes porosity, which is responsible for the improved ductility.     

新型镁合金大变形技术的研究与验证

研究了一种正挤压与等通道挤压相结合的新的Extrusion-Shearing(ES)变形方法。应用有限元法对ES变形过程进行了计算机模拟,表明ES技术可以大大提高累积应变和动态再结晶晶粒的体积分数。在Gleeble1500热模拟机上安装ES成形模具,对ES成形挤出的棒料进行微观组织观察,并对热模拟的数据进行处理。结果表明,ES成形可以细化晶粒并提高成形的均匀性。计算机模拟和热模拟实验表明,ES成形是一种新型的镁合金大塑性变形方法,可以有效细化晶粒、提高组织的均匀性     

Effect of extrusion ratio on microstructure and mechanical properties of AZ91D magnesium alloy recycled from scraps by hot extrusion

A method for recycling AZ91D magnesium alloy scraps directly by hot extrusion was studied. Various microstructural analyses were performed using the techniques of optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy(EDS). Microstructural observations revealed that all the recycled specimens consisted of fine grains due to the dynamic recrystallization. The main strengthening mechanism of the recycled specimen was grain refinement strengthening and homogeneous distribution of oxide precipitates. The interfaces of individual scraps of extruded materials were not identified when the scraps were extruded with the extrusion ratio of 40:1. Oxidation layers of the scraps were broken into pieces by high compressive and shear forces under the extrusion ratio of 40:1. The ultimate tensile strength and elongation to failure increased with increasing the extrusion ratio. Recycled specimens with the extrusion ratio of 40:1 showed higher ultimate tensile strength of 342.61 MPa and higher elongation to failure of 11.32%, compared with those of the cast specimen.     

连续挤压工艺生产AZ31镁合金板材的实验研究

本文利用连续挤压技术的单、双杆进料方法试验生产了尺寸为160mm×8mm, 170mm×4mm和160mm×3mm的AZ31镁合金板材。分析了单、双杆进料方式,不同宽厚比和不同挤压速度等条件对镁合金板材横截面微观组织及力学性能的影响。讨论了应用双杆进料连续挤压工艺生产AZ31镁合金宽薄板的工艺可行性。结果表明：与单杆进料相比,双杆进料方式的连续挤压AZ31镁合金板材横截面微观组织均匀性较好,板材平均抗拉强度可达到239MPa,平均延伸率为15%。宽厚比由20增加到53,可获得5μm细化晶粒的镁合金板材。随挤压轮转速提高,板材抗拉强度降低,是由于温度升高会导致晶粒尺寸变大。     

Influence of homogenizing on mechanical properties of as-cast AZ31 magnesium alloy

Forward extrusion experiments of as-cast AZ31 magnesium alloy were conducted at different temperatures and different extrusion ratios using the as-cast billets with and without homogenizing treatment. The mechanical properties of pre- and post-extrusion of the two kinds of billets were investigated. Experimental results show that the mechanical properties of post-extrusion of the two kinds of billets all are obviously improved compared with those of pre-extrusion. The elongation of post-extrusion using the billet with homogenizing is higher than that without homogenizing, but the tensile strength is lower than that without homogenizing. When the extrusion ratio increases, the elongation and tensile strength of post-extrusion of two kinds of billets all will increase obviously. When the extrusion temperature of billet without homogenizing increases, the tensile strength of post-extrusion will decrease obviously and the elongation of post-extrusion will change to a small extent. For the billet with homogenizing, the tensile strength of post-extrusion will decrease in some sort when extrusion temperature increases.     

AZ91D镁合金屑的固相再生(英文)

利用固相再生技术回收利用AZ91D镁合金屑,具体工艺为先冷压再热挤。结果表明:制备的AZ91D镁合金具有较好的力学性能且晶粒明显细化。在热挤出过程中发生了动态再结晶,且动态再结晶组织受到热挤温度和应变速率的影响,在300-350 °C下基面滑移和孪晶协调变形导致动态再结晶晶粒产生,形成"项链"组织;在 350-400 °C下位错的交滑移控制动态再结晶形核;高于400 °C时位错攀移控制了整个动态再结晶过程,形成均匀的再结晶组织。随着应变速率增加AZ91D镁合金力学性能增大,改善了材料的力学性能,但应变速率过大,制备试样表面出现裂纹,影响材料的力学性能。     

Solid-state recycling of aluminium alloy swarf through cold profile extrusion and cold rolling

In this study, the possibility of solid-state recycling of aluminium alloy machining swarf using cold extrusion and a subsequent cold rolling process is investigated. Cast Al-Si alloy swarf was cold compacted into billets and successfully profile-extruded into square bars with a rectangular cross-sectional aspect ratio of 1:1.8 under an extrusion ratio of 4 or more. After annealing, the extruded bars underwent multi-pass cold rolling into 1-mm thick strips with a total rolling reduction of 85%. Optical microscopy demonstrated that in material recycled using only an extrusion process, coarse residual voids existed in regions where insufficient plastic strain was introduced, causing a visible expansion of the material during heat treatment. However, uniaxial tensile tests showed that extrusion-recycled material had a higher mechanical strength than the original aluminium alloy, implying sufficient bonding among the individual pieces of machining swarf. It was also found that the strength and density of material recycled through extrusion and an additional rolling process were superior to material recycled using extrusion only. Moreover, it was observed that the ductility of the recycled materials was inferior to that of the original aluminium alloy.     

Solid-state recycling of AZ91D magnesium alloy chips

A method for recycling AZ91D magnesium alloy chips by solid-state recycling was studied. The experiments were carried out adopting the cold-press pressure and hot extrusion. The results indicate that recycled specimens of AZ91D magnesium alloy present better mechanical properties and consist of fine grains due to dynamic recrystallization. The mechanisms of dynamic recrystallization depend on plastic deformation process and change with the deformation temperature. At 300-350 °C, the deformation mechanisms are associated with the operation of basal slip and twinning, and the “necklace” structures are formed. At 350-400 °C, the cross slip results in the formation of new grains and grain refinement. At above 400 °C, the dynamic recrystallization mechanisms are controlled by dislocation climb, and recrystallized grains are homogeneous. The tensile strength of recycled specimens increases with the increase of the strain rate. When the strain rate is overhigh, the cracks and fractures in the surface appear and affect the tensile strength of recycled specimens.     

Structure and mechanical properties of AZ31 magnesium alloy billets by different hot-top semi-continuous casting technology

AZ31 alloy billets of 200 mm in diameter were produced by three different processes of conventional direct chill(DC) casting,low-frequency electromagnetic casting(LFEC) and low-frequency electromagnetic vibration casting(LFEVC),respectively.The effect of LFEC and LFEVC on the microstructures,macrosegregation and mechanical properties of AZ31 alloy billets was investigated.In conventional DC casting,the AZ31 alloy billets exhibited coarse grains(about 370 μm) and severe segregation of Al and Zn.In the presence of a solo low-frequency alternating magnetic field or a low-frequency electromagnetic vibration field applied during DC casting of φ200 mm AZ31 billets,grains in the AZ31 alloy billets were effectively refined(about 210 μm) and the macrosegregation of Al and Zn in the billets was greatly decreased.Furthermore,the tensile strength,fracture elongation and hardness of the as-cast AZ31 alloy billets were improved by the processes of LFEC and LFEVC relative to that cast by the process of conventional DC casting.     

AZ91镁合金齿轮类精密零件超塑性模锻成形研究

以开发镁合金精密零件超塑性成形技术为目标,以铸态AZ91镁合金为实验材料,采用等径角挤压工艺对合金进行了组织细化,并用所制备的细晶材料为坯料对两种齿轮类精细零件进行了超塑性成形实验。研究结果表明,AZ91镁合金经过4道次等径角挤压,可以获得晶粒尺寸为2μm~5μm的细晶组织材料。将这种细晶组织材料进行超塑性成形,可以获得轮廓清晰、尺寸精度良好的精密齿轮和铰接杆零件。     

电磁场施加方式对半连续铸造镁合金锭坯组织与性能的影响

采用不同电磁场施加方式和半连续铸造制备Φ200 mm AZ31镁合金锭坯.研究电磁场施加方式对AZ31锭坯微观组织和力学性能的影响.结果表明,与常规直接水冷半连铸锭坯相比,单感应线圈通电(LFEC)或两组感应线圈同时通电(LFEVC)来铸造锭坯时,组织细化,第二相(β-Mg17Al12)变得细小弥散,锭坯横截面边部与中心部位晶粒大小差别明显降低,LFEVC铸造的锭坯比LFEC铸造的更为明显;两种电磁场施加方式均有利于主合金元素在锭坯中均匀分布,宏观偏析在很大程度上得到抑制;两种电磁场施加方式均有利于锭坯的力学性能的提高,与常规铸造相比,屈服强度和抗拉强度分别提高50～60 MPa和40～50 MPa,延伸率也增大1倍.     

High quality extrudates from aluminum chips by new billet compaction and deformation routes

The effects of different billet preparation techniques as well as selection of various deformation routes and their influence on the final mechanical properties in chip extrusion was studied. The AA6060 chips were compacted into billets using various techniques and then extruded through the flat-face, porthole and ECAP dies to create different deformation routes. The microstructures and the mechanical properties of the chip extruded profiles were compared to cast billets extruded through the flat-face die under the same conditions. The proposed technology shows very promising results in terms of energy savings and production of the high quality engineered aluminum profiles.     

Effect of heat treatment on the distribution and volume fraction of Mg2Si in structural aluminum alloy 6063

The structure and properties of an aluminum alloy after extrusion in cast and homogenized states are studied. Commercial billets are melted in a horizontal continuous casting installation. After homogenizing the billets are used for fabricating shapes of specified form in an extrusion press. The shapes are subjected to final aging. The volume fraction and the distribution of the second Mg₂Si phase are determined after different kinds of treatment. The structure and mechanical properties of shapes obtained from cast and homogenized billets are compared after aging and without aging. The effect of homogenizing on the properties of the alloy after extrusion is analyzed. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 17–21, May, 2006.     

挤压比对热挤压AZ80镁合金管材组织和性能的影响

选用不同的挤压比对变形镁合金AZ80进行管材热挤压工艺试验研究,对挤压前后材料组织与力学性能的变化进行分析。结果表明,热挤压可以显著细化AZ80镁合金的晶粒,而且随着挤压比的增加,晶粒变得更加细小;增大挤压比也可以提高AZ80镁合金的抗拉强度和屈服强度。结果表明,挤压比为18.2,坯料温度为390℃,模具预热温度为360℃,凹模的半模角为60°～70°,可得到均匀的合金组织和良好的力学性能。     

Effect of Heat Treatment on Microstructure and Mechanical Properties of ZM6 Alloy Prepared by Solid Recycling Process

ZM6 magnesium alloy was prepared by solid recycling process. Effect of heat treatment on microstructure and mechanical properties of the alloy was investigated. Cold pressing was employed to prepare extrusion billets of ZM6 chips, then the billets were hot extruded at 773 K with an extrusion ratio of 25:1. During hot extrusion, the grains refined and the particles were broken. The peak-aging materials showed fine plate-shaped β′ precipitates. The ultimate tensile strength and elongation to failure of as-extruded rods was 232.2 MPa and 23%, respectively. After T5 and T6 heat-treatment, obvious improvement of the tensile strength was obtained because of dispersive particles or fine precipitates. The morphology of the fracture surfaces was examined by employing scanning electron microscope.