等径角挤压处理后的Mg-Gd-Y-Zr合金的微观组织和力学性能

研究等径角挤压过程中材料的微观组织和织构演变以及对其力学性能的影响。结果表明：挤压4道次后的微观组织是不均匀的,即在此过程中形成了粗晶区和细晶区2个区域。颗粒诱发的再结晶机制导致晶粒细化,在4道次后形成了更加随机的织构。与挤压前的原始材料相比较,经等径角挤压处理的材料虽然强度没有增加,但是塑性有了显著的提高。用织构改变和第二相颗粒解释了合金塑性的变化。     

Mechanical properties at room temperature of an Al-Zn-Mg-Cu alloy processed by equal channel angular pressing

Tensile tests were conducted to evaluate the influence of equal-channel angular pressing (ECAP) on the mechanical properties at room temperature of overaged Al 7075-O alloy. ECAP processing was performed using route B_C at different temperatures and number of passes, i.e. different processing severity conditions. The maximum load (F_max) recorded during the last pass of each ECAP path considered in this study is a very good estimation of the processing severity. The mechanical properties were studied in terms of the balance between tensile strength and ductility. In the processed Al 7075-O alloy, the grain size was reduced down to ∼150 nm. Consequently, tensile testing at room temperature revealed a significant increase in the maximum tensile strength after ECAP with respect to the as start material. In the present study, as the processing severity increases with the number of ECAP passes or with the decrease in processing temperature, there is a consistent trend of increment in ultimate tensile strength with minor decrease in uniform plastic elongation respect to the first ECAP pass at room temperature. This is in contrast to the behaviour after more severe plastic deformation conditions, where an increase in strength together with a strong decrease in elongation would be expected.     

Effects of Cu and Mn on mechanical properties and damping capacity of Mg-Cu-Mn alloy

The effects of Cu and Mn additions on mechanical properties and damping capacity of Mg-Cu-Mn alloy were investigated. The tensile properties and damping capacity at room temperature of as-cast Mg-Cu-Mn alloy were tested.The microstructurc was studied using optical microscope,X-ray diffraction and scanning electron microscope.The Hall-Perch relation and Granato-Lücke model were used to explain the influences of Cu and Mn additions on the tensile properties and damping capacity of Mg-Cu-Mn alloy.The result...     

Effects of die angle on microstructures and mechanical properties of AZ31 magnesium alloy processed by equal channel angular pressing

1　INTRODUCTIONMagnesiumalloysarethelightestmetallicstruc turalmaterialsandhencetheyprovidegreatpotentialintheweightsavingofautomotiveandaerospacecomponents ,materialhandlingequipment ,portabletoolsandevensportinggoods[1,2 ] .Duetotheirhexago nalclose packed (HCP)crystalstructure ,magnesiumalloysperform poorformabilityandlimitedductilityatroomtemperature ,thustheirproductsaremainlyfabricatedbycasting ,inparticular ,die casting ,andtheapplicationsofwroughtmagnesiumalloysarelim ited .Nowit…     

等通道转角挤压Mg-3.52Sn-3.32Al合金的组织与力学性能

采用等通道转角挤压（ECAP）Bc路径对固溶态Mg-3.52Sn-3.32Al合金分别挤压1、4和8道次。利用光学显微镜、扫描电子显微镜、透射电子显微镜和X射线衍射仪分析合金的组织和相组成,并测试了其室温拉伸力学性能。结果表明,经ECAP挤压后,固溶态合金组织中析出大量细小的Mg2Sn相和极少量的Mg17Al12相。随挤压道次增加,合金的综合力学性能先提高后降低。经4道次挤压后,合金的综合拉伸力学性能相对较佳,抗拉强度、伸长率和硬度分别达到250 MPa、20.5%和61.3 HV9.8,较未ECAP时分别提高43.7%、105%和26.9%。经ECAP挤压的合金室温拉伸断口均呈韧性断裂。等通道转角挤压Mg-3.52Sn-3.32Al合金的力学性能受晶粒尺寸、析出相以及组织织构的共同影响。     

等通道转角挤压Al-Cu合金的冲击性能

对铸态Al-0.63%Cu和Al-3.9%Cu(质量分数)合金进行等通道转角挤压处理,研究了Al-Cu合金冲击性能的变化.结果表明,等通道转角挤压增强了Al-0.63%Cu合金的冲击性能;而对于Al-3.9%Cu合金,虽然晶粒细化和第二相的弥散分布使其强度增加,但较多的第二相θ(Al2Cu)未提高其冲击性能.该合金的冲击吸收功与其静力韧度有关.     

Microstructure evolution and mechanical behavior of AZ31 Mg alloy processed by equal-channel angular pressing

AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP, in placing of planes and become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane (0001).     

等通道转角挤压制备超细晶Mg15Al双相合金组织与性能

对高铝双相合金Mg15Al在553K以Bc路线进行了不同道次的等通道挤压(ECAP),获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm～200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32.04%,抗拉强度σb从150MPa提高到269.3MPa,延伸率δ由0.05%提高到7.4%;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。     

Microstructure and mechanical properties of 7005 aluminum alloy processed by one-pass equal channel reciprocating extrusion

An equal channel reciprocating extrusion (ECRE) was proposed first to obtain a severe plastic deformation (SPD) of 7005 alloy. The microstructure and mechanical properties of one-pass ECREed (ECRE processed) 7005 alloy were investigated. The results show that SPD occurring in ECRE leads to a mixed microstructure. ECREed 7005 alloy exhibits a significant improvement of ultimate tensile strength (UTS) and elongation. Mechanical properties in the region undergoing a complete ECRE process are higher than those in the region undergoing an incomplete ECRE process due to larger dislocation strengthening effect. Yield strength (YS) and UTS first decrease and then increase with an increase of extrusion temperature. The YS of 359.2 MPa, UTS of 490 MPa and elongation of 17.7% are obtained after T6 treatment. Fine-grain strengthening, dislocation strengthening and precipitation strengthening in the T6-treated ECREed sample all play important roles in improving the mechanical properties.     

等径角轧制AZ31镁合金板材的组织与性能

采用等径角轧制工艺制备了AZ31镁合金板材.结果表明:经等径角轧制后的板材,晶粒取向由等径角轧制前的(0002)基面取向演化为基面与非基面共存的取向.与等径角轧制前的板材相比,板材晶粒尺寸略有长大并有孪晶出现,但强度却明显提高,而断裂延伸率变化不大,尤其是1个道次轧制的板材其抗拉强度由等径角轧制前的240增大到275 MPa,屈服强度由193.8增大到239.2 MPa;随着等径角轧制道次的增加,板材的强度逐渐降低,至第4个道次其抗拉强度仅为250 MPa,屈服强度为207.3 MPa.     

Microstrucmre and mechanical properties of AZ31-0.5%Si alloy processed by ECAP

Microstructure and mechanical properties of AZ31-0.5%Si（mass fraction） alloy processed by ECAP were investigated. Results show that Mg2Si phase formed during solidification can be broken up and be dispersed in matrix by ECAP. With the increase of ECAP passes, Mg2Si phase in microstructure tends to distribute uniformly. The mean grain size is about 4 μm, and the mean size of Mg2Si is about 6 μm. The elongation of AZ31-0.5%Si alloy is significantly increased after ECAP and then changes a little with increasing ECAP passes, The ultimate strength of as-extruded AZ31-0.5%Si alloy reaches 348.9 MPa, while its strength decreases after ECAP.     

等径弯曲通道变形制备高性能Cu-Cr合金的组织性能

用两种方式等径弯曲通道变形(equal-channel angular pressing,简称ECAP)制备了的具有等轴晶组织的超细晶Cu-0.4Cr合金,晶粒尺寸为500nm。研究了不同挤压方式、不同挤压道次合金的组织和性能的变化。探讨了不同退火温度对5～8道次材料导电率和硬度的影响。结果表明,经ECAP挤压后的Cu-0.4Cr合金具有很好的综合性能,拉伸强度可达565MPa;硬度和导电率分别为225 HV和66.4%IACS;723K退火1h后材料的导电率和硬度可达80.3%IACS和210.9HV;软化温度可达723K。     

Low-temperature superplasticity of ZK40 magnesium alloy processed using equal channel angular pressing

Microstructure evolution and superplastic behaviors of ZK40 magnesium alloy were investigated in the temperature range of 473～623 K. Transmission electron microscopy (TEM) was used to study the microstructure changes, twinning occurred significantly after being processed by equal channel angular pressing (ECAP) for one pass through the die, the mean grain size was 5.6μm. Finer grains can be obtained after further processing through ECAP, the average grain size of the alloy processed by ECAP for three passes was as low as 0.8 μ_m; this alloy exhibited low temperature superplasticity at 473～523 K, elongations obtained at the same initial strain rate of 1×10~(-3) s~(-1) were 260％ at 473 K and 612％ at 523 K, respectively. Corresponding values for the ZK40 alloy processed by ECAP for only one pass were 124％ at 473 K and 212％ at 523 K, respectively; poor superplastic behavior of this material was related to the long-range stresses associated with the non-equilibrium grain boundaries within the coarse grains. The incompatibility between fine and coarse grains was thought to be unfavorable to the improvement of superplasticity.     

等通道转角挤压高铝镁合金的微观组织和力学性能

对三种铸态高铝镁合金进行了等通道转角挤压(ECAP),对挤压前后的微观结构和力学性能进行了测试.结果表明挤压使合金组织显著细化,力学性能明显提高.由于高铝镁合金在高温挤压过程中除α-Mg基体相外,存在较多β-Mg17Al12,两相相互制约,显著降低各相的(动态)再结晶速率,从而容易获得比常规Mg-Al系合金细小得多的组织.结合等通道挤压加工,有望发展高铝镁合金为经济型高强度镁合金.     

High strain rate superplasticity at intermediate temperatures of the Al 7075 alloy severely processed by equal channel angular pressing

The mechanical properties of an overaged Al 7075-O alloy processed by ECAP were examined by tensile tests at intermediate-high temperatures ranging from 250 to 400 °C and strain rates from 10⁻⁵ to 10⁻¹ s⁻¹. The influence of the number of ECAP passes on the ductility enhancement was evaluated. Elongation to failure, e_F, significantly increased with increasing the number of ECAP passes up to 8 at 130 °C. The alloy processed under these conditions exhibited a maximum value of 322% at 300 °C and an initial strain rate of 10⁻³ s⁻¹. High strain rate, e_F = 210%, at a strain rate as high as 10⁻² s⁻¹. The large elongations together with lower stresses and lower stress exponents than those for the start material confirm that grain boundary sliding (GBS) is the operative deformation mechanism. A loss of superplastic behaviour at temperatures above 350 °C is related to abnormal grain growth and a change of deformation mechanism.     

T型通道挤压变形ZK60镁合金的组织与力学性能

采用一种新型剧塑性变形工艺—T型通道挤压(TCP)对ZK60镁合金在673K下以A和Bc两种路径进行1～4道次挤压变形,通过光学显微镜观察变形镁合金的显微组织,并对TCP变形镁合金的不同部位在应变速率4×10-3s-1时进行室温拉伸性能测试.结果表明塑性变形最大的部位是试样中间部位的最底部,其组织特征为细小晶粒包围着大晶粒,大晶粒呈拉长的流线状;4道次变形后,A路径的平均晶粒尺寸由退火态时的88.5μm细化至2.4μm,Bc路径的平均晶粒尺寸则细化至4.6μm,但组织更均匀;同时,在相同道次TCP变形后,A路径变形合金的屈服强度都高于Bc路径变形合金的,但前者的抗拉强度和塑性却低于后者的;此外,试样最底部的抗拉强度和屈服强度均高于试样顶部的,经Bc路径2道次变形后试样底部与顶部的抗拉强度和屈服强度分别相差39.5和43.1Mpa,而经4道次变形后试样两个部位的抗拉强度和屈服强度分别只相差21.2和11.7Mpa.     

等通道转角挤压7075铝合金动态再结晶组织晶粒度预报

采用等通道转角挤压(ECAP)对7075铝合金试样进行挤压,利用有限元软件对ECAP的连续动态再结晶组织晶粒度进行预报,采用有限元和实验相结合的方法,研究不同挤压道次对7075铝合金A路径ECAP过程组织晶粒度的影响。模拟结果表明,经过一道次、二道次和四道次A路径ECAP后试样中心区域的晶粒尺寸分别为24.8μm、20.2μm、16.7μm,晶粒随着挤压道次的增加不断细化。通过金相定量法计算可得一道次、二道次和四道次A路径ECAP实验后试样中心区域的晶粒度分别为26μm、20μm、16μm,与有限元预报结果吻合良好,最大误差小于5%,证明基于连续动态再结晶模型的有限元预报准确性较高。     

镁合金等通道转角挤压过程中的晶粒细化机制

采用金相显微镜、背散射电子衍射(EBSD)和透射电子显微镜(TEM)分析ZK60镁合金在等通道转角挤压(ECAP)过程中不同部位的显微组织特征。结果表明:ZK60镁合金经240℃ECAP变形1道次后,合金的晶粒得到明显细化,但组织仍不均匀。剪切变形前,合金组织主要为粗大晶粒并伴有大量孪晶,剪切区的组织主要为剪切变形带和少量再结晶组织;剪切变形后,合金的晶粒组织主要为再结晶组织;合金ECAP过程的晶粒细化主要为机械剪切和动态再结晶的综合作用。     

通道间隙对等径角轧制AZ31镁合金板材组织与性能的影响

研究了不同通道间隙下,AZ31镁合金板材在等径角轧制过程中晶体取向的演化特征以及通道间隙对其显微组织和力学性能的影响.X射线衍射分析表明在等径角轧制过程中,随着通道间隙的减小,晶体取向变化加大,(0002)基面取向减弱.等径角轧制后,孪晶明显增多,且随着通道间隙的减小,孪晶数量逐渐增多.单向拉伸试验表明,等径角轧制后的板材,其变形行为和力学性能存在明显的各向异性特征,与等径角轧制前的板材相比,在轧向其屈服强度明显降低由轧制前的240MPa降至155MPa,抗拉强度略有增加,但随着通道间隙的减小,断裂延伸率略有增大;在横向其屈服强度和抗拉强度均增大,随着通道间隙的减小,屈服强度和抗拉强度略有减小,但断裂延伸率增大.     

Tensile properties of 2024 Al alloy processed by enhanced solid-solution and equal-channel angular pressing

Equal-channel angular pressing（ECAP） of an enhanced solid-solution treated 2024 Al alloy was successfully performed at room temperature, with an imposed equivalent normal strain of about 0.5. A very high hardness about HV191 and yield strength about 610 MPa （30% higher than those of the unECAPed 2024 Al alloy） in terms of commercial aluminum alloys were observed for the ECAPed 2024 Al alloy. In addition to the strengthening, this process allows the ECAPed 2024 Al alloy have a moderate level of tensile ductility （about 12.7%） and a significant strain hardening capability up to tensile failure. After aged at 373 K for 48 h, the ECAPed alloy increases its hardness （about HV201） and tensile ductility （about 14 %） further. The TEM results show that the ECAPed 2024 AI alloy presents a plate structure （about 50-100 nm） with high density of dislocation and additional thin plate （approximately 〈10 nm= inside. The XRD results show that the ECAP processing decreases the texture and increases the dislocation density of the alloy considerably. The theoretical calculations show that the increase of dislocation density resulting from ECAP processing makes a considerable contribution about 55.2 % for the improvement of yield strength.