稀土Mg-Mn-Zn-Ce合金等通道转角挤压工艺

为获得性能良好的超细晶镁合金材料,采用等通道转角挤压工艺对稀土Mg—Mn—Zn—Ce合金进行塑性加工,研究了速度、温度和润滑条件对合金的挤压工艺以及性能的影响。实验结果表明：对于稀土Mg—Mn—Zn-Ce合金,等通道转角挤压的润滑剂为7025高温润滑脂,速度2mm／s,第一道次的挤压温度为250℃,第二道次的挤压温度为270℃。该工艺条件使等通道转角挤压能够顺利进行,可获得表面光滑平整、晶粒组织细化的稀土Mg—Mn—Zn—Ce合金。     

AZ31镁合金等通道转角挤压工艺优化与实验研究

通过等通道转角挤压工艺细化镁合金晶粒提高镁合金塑性的研究受到众多学者的高度重视。本文通过有限元数值模拟分析了不同模具几何形状等工艺参数对镁合金剧烈塑性变形过程的重要影响,研究了模具几何形状对挤压件应力分布的影响规律。为了实现镁合金块体金属材料的反复挤出,使挤压件获得足够变形达到晶粒细化的目标,本文通过改进具有预应力结构的模具,实现了等通道转角温挤压工艺,为镁合金剧烈塑性变形的机理和实验提供可靠的理论依据和指导。     

等通道转角挤压后AZ31镁合金的微观结构与性能

为了进一步探讨细晶镁合金的制备方法与性能 ,采用模角φ =12 0°的模具、以BC路径对AZ31镁合金进行了等通道转角挤压试验研究 ,对挤压过程中各道次试样的微观结构及性能进行了分析测试 .结果表明 ,随着挤压道次的增加 ,晶粒得到不断细化 ,力学性能也发生显著的变化 ;当挤压 12道次时 ,总的等效应变量约为 8,晶粒得到显著细化 ,晶粒尺寸为 1～ 5μm ,但合金的抗拉强度变化不大 ,屈服强度则有所下降 ,约为 10 0MPa ,延伸率则提高到 4 5 %以上     

不同路径等通道转角挤压镁合金的结构与力学性能

为了研究等通道转角挤压时不同工艺路径对镁合金微观结构及性能的影响 ,采用模角φ =12 0°的模具 ,以A ,BA,BC,C四种工艺路径对AZ31镁合金进行了等通道转角挤压 ,分析测试了室温下挤压试样的微观结构及性能 .结果表明 ,相比于A ,BA,C路径挤压 ,BC 路径挤压容易实现较多的挤压道次和变形量 ;多道次挤压后 ,镁合金的晶粒得到显著细化 ,力学性能也显著改善 ,但不同路径的影响不同 .当挤压 12道次时 ,BC,BA 路径挤压试样的屈服强度显著下降 ,延伸率大幅度提高 ;A ,C路径挤压试样的屈服强度变化较小 ,延伸率的提高幅度也小 .     

等通道转角挤压对铝青铜力学性能的影响

采用等通道转角挤压（ECAE）工艺对铝青铜(Cu 10%Al 4%Fe)进行热处理,研究了ECAE处理工艺中预热温度、挤压道次及退火处理对铝青铜外观形貌、微观组织及力学性能的影响.结果表明:在650 °C的预热温度下,铝青铜可以顺利通过ECAE挤压通道;随着ECAE挤压道次从1增至4,铝青铜的显微硬度、屈服强度及延伸率显著增加;经500 °C退火60 min处理后,铝青铜的力学性能最佳.     

等通道转角挤压对铝青铜合金组织及摩擦学性能的影响

对铝青铜合金(Cu-10%Al-4?)进行了等通道转角挤压(ECAE)热加工处理,研究了ECAE对合金微观组织、力学性能及摩擦学性能的影响.结果表明:ECAE热挤压后合金的晶粒显著细化,晶粒尺寸随着挤压道次的增加而逐步减小;晶粒细化导致合金的硬度与屈服强度显著增加,提高了合金抵抗塑性变形能力,减轻了磨粒对合金表面的犁削作用;ECAE热挤压细化了合金中的第二相,减小了脱落硬质颗粒压入合金表面的深度与宽度,降低了合金的磨损量,提高了合金的摩擦学性能.     

ECAP挤压L2纯铝的微观组织演化规律

用等通道转角挤压对纯铝L2进行10道次挤压,结果表明：挤压1道次后,原来晶粒尺寸为1 mm的等轴晶沿剪切方向被拉长为条带状晶,在条带状晶粒之间出现被剪切破碎的细小亚晶粒.挤压2道次后,出现了少量等轴晶.挤压4道次后,晶粒取向性变得不太明显,小角度晶界的亚晶粒逐步向大角度晶界的等轴晶演化,晶粒细化到1 μm.随挤压道次的继续增加,晶粒大小不再变化,而形状向等轴状演化.挤压10道次后,合金组织由晶粒大小为1 μm的等轴晶组成.ECAP挤压中,纯剪切变形和应变量的双重作用导致晶粒细化.当晶粒尺寸小于临界尺寸时,剪切变形对晶粒的细化起主要作用;当达到临界尺寸后,应变量起主要作用,表现在使合金组织形貌向等轴晶转变.     

挤压速度对Ti6Al4V钛合金等通道转直角挤压过程 影响的数值模拟

采用Deform-3D有限元软件,对样品初始温度为900℃的Ti6Al4V钛合金等通道转直角挤压在0~5 mm/s的下压速度范围内进行了数值模拟。模拟计算结果表明：在相同的挤压速度下,试样通过转角后的温度降低速率减小;挤压速度越大,挤压过程所需的荷载越低,应变累积越小,等效应力越低,应力集中现象越少,挤压过程中试样的温降越小;本研究条件下,挤压速度值选定为5 mm/s。     

等通道转角挤出制备自增强高密度聚乙烯

采用等通道转角挤出（ECAE）方法对高密度聚乙烯（HDPE）进行自增强挤出，研究挤出工艺条件与材料结构、性能之间的关系．利用广角X射线衍射（WAXD）、差示扫描量热分析（DSC）等手段对材料结构进行表征，结果表明：经过等通道转角挤出后，HDPE的结晶度提高、晶粒细化，抗拉强度提高了23％．     

等通道转角挤压（ECAE）对聚（D，L-）乳酸弯曲性能的研究

采用等通道转角挤压技术对聚(D,L-)乳酸(PDLLA)进行塑性变形.与压制成型工艺比较,ECAE对样品的弯曲性能有明显影响.随着转角挤压温度的提高,聚(D,L-)乳酸材料的弯曲强度逐渐增大,当温度为75℃时,其弯曲强度σ_b达到最大值164 MPa.聚(D,L-)乳酸等通道转角挤压后,断裂机理由脆性断裂转变为韧性断裂,形成韧性断裂断口形貌.     

Damage prediction of 7025 aluminum alloy during equal-channel angular pressing

Equal-channel angular pressing (ECAP) is a prominent technique that imposes severe plastic deformation into materials to enhance their mechanical properties. In this research, experimental and numerical approaches were utilized to investigate the mechanical properties, strain behavior, and damage prediction of ECAPed 7025 aluminum alloy in various conditions, such as die channel angle, outer corner angle, and friction coefficient. Experimental results indicate that, after the first pass, the yield strength, ultimate tensile strength, and hardness magnitude are improved by approximately 95%, 28%, and 48.5%, respectively, compared with the annealed state, mainly due to grain refinement during the deformation. Finite element analysis shows that the influence of die channel angle is more important than that of outer corner angle or friction coefficient on both the strain behavior and the damage prediction. Also, surface cracks are the main cause of damage during the ECAP process for every die channel angle except for 90°; however, the cracks initiated from the neighborhood of the central regions are the possible cause of damage in the ECAPed sample with the die channel angle of 90°.     

Improvement of pitting corrosion resistance for Al-Cu alloy in sodium chloride solution through equal-channel angular pressing

Significant corrosion resistance improvement was achieved in solid-solution treated (T4) Al-Cu alloy after severe grain refinement through equal-channel angular pressing. The bulk ultrafine-grained Al-Cu alloy with grain sizes of 200 ? 300 nm has higher pitting potential (elevated by about 34 mV, SCE) and lower corrosion current density (decreased by about 3.88 μA/cm²) in polarization tests than the as-T4 alloy, and increased polarization resistance (increased by about 5.7 k ?·cm²) in electrochemical impendence spectrum tests, along with alleviated corrosion damage in immersion tests. Two factors responds to the improved corrosion resistance of the alloy: the first is the refinement of residual θ -phase (Al2Cu) particles leading to the lower micro-galvanic currents and reduced susceptibilities to pitting corrosion, the second is the mass of strain-induced crystalline defects provid ing more nucleation sites for the formation of more volume fractions of stable oxide film.     

Improvement of pitting corrosion resistance for Al-Cu alloy in sodium chloride solution through equal-channel angular pressing

Significant corrosion resistance improvement was achieved in solid-solution treated(T4) Al-Cu alloy after severe grain refinement through equal-channel angular pressing.The bulk ultrafine-grained Al-Cu alloy with grain sizes of 200-300 nm has higher pitting potential(elevated by about 34 mV,SCE) and lower corrosion current density(decreased by about 3.88μA/cm~2) in polarization tests than the as-T4 alloy,and increased polarization resistance(increased by about 5.7 kΩ·cm~2) in electrochemical impendence s...     

强化固溶态2024铝合金ECAP加工后的拉伸性能

在室温下对经强化固溶处理的2024铝合金实施了等效应变为0．5的等通道转角挤压（ECAP）,将强化固溶、形变、时效和晶界细化四者有机结合,制备出超高强铝合金,其硬度、屈服强度、伸长率分别高达约191HV,610MPa和13％．强度-结构关系的定量计算表明,ECAP变形过程中所引入的位错,其对强度提升的贡献高达整个强度提高值的62．2％．研究结果还表明,强化固溶→低温ECAP变形→低温人工时效是提升常规铝合金的强度、制取超高强铝合金的一条有效途径。     

400℃退火对ECAP形变Q235钢的强度和位错强化的影响

将经过淬火预处理和等通道转角挤压加工(ECAP)的Q235钢进行400℃退火.采用拉伸试验、X射线衍射(XRD)分析及描述强度-位错密度关系的Taylor公式,研究400℃退火对ECAP形变低碳钢的强度和位错强化的影响.拉伸试验表明:400℃退火使ECAP形变Q235钢强度降低,屈服强度从825 MPa下降到725 MPa,加工硬化能力和塑性显著提高.基于XRD分析和Taylor公式的定量计算说明,400℃退火对ECAP形变Q235钢的位错强化影响很小,实际强度的降低不是来自于位错强化的降低,而是来自于其他强化机制(晶界、亚晶界等)的降低.     

工业纯铝等径弯曲通道变形过程的数值模拟

等径弯曲通道变形(Equal ChannelAngularPressing简称ECAP)由于能直接制备块状超细晶材料而备受关注。通过对工业纯铝的ECAP变形过程进行有限元数值模拟,获得了变形过程的载荷变化规律和等效应变分布规律,并用坐标网格法对模拟结果进行了实验验证。在摩擦条件下,试样中区下表面的等效应变最大,至上表面处等效应变为最小。而在无摩擦理想情况下,其等效应变分布恰好相反,这可能是由于试样在ECAP变形过程中所受应力场和应变场的不同引起的。     

采用ECAP制备亚微晶铝合金及其力学性能

采用ECAP与热处理工艺相结合制备了亚微晶7050和2224铝合金,并研究了力学性能·结果发现,ECAP后进行固溶和时效处理,晶粒细化到06μm;力学性能明显提高,7050合金的抗拉强度σb为616MPa,延伸率δ为17%,2224合金的抗拉强度σb为618MPa,延伸率δ为12%,成为亚微晶超高强铝合金     

等径角挤压对纯铜组织与性能的影响

研究采用BC路径(即试样进入下一道次挤压时按同一方向旋转90°)对纯铜进行等径角挤压后得到的组织与性能.结果表明,通过室温下对纯铜的8道次挤压后,得到均匀、细小的等轴晶组织(晶粒尺寸约1.5μm).抗拉强度从原来的235 MPa提高到420 MPa,硬度从114 HV提高到184.3 HV,延伸率由原来的45%降低到19%.通过对不同挤压道次试样在473 K下60 min的退火处理后,其晶粒进一步细化至1μm,其抗拉强度提高到435 MPa.     

Severely deformed copper by equal channel angular pressing

Mechanical and microstructural analysis of equal channel angular pressed copper was experimentally investigated. The results showed that the hardness distribution uniformity was rapidly decreased after the first pass and gradually improved at the following passes. Also, the bottom region of the pressed material experienced lower Vickers hardness magnitude irrespective of pass number. Furthermore, the addition of 0.1% magnesium to the pure copper had a considerable effect on the distribution uniformity. In addition, the material fracture mode changed from ductile to brittle by the alteration of the dimples to cleavage planes mechanism. Moreover, the formability index was dramatically reduced after the first pass and slowly improved at the succeeding passes. Eventually, ECAP process led to the increment of low angle grain boundaries and the decrease of high angle grain boundaries at the initial passes and vice versa at the subsequent ones.