挤压工艺对6061-T6铝合金棒材力学性能和粗晶环的影响

采用正交试验方法研究了挤压工艺对6061-T6铝合金棒材力学性能和粗晶环深度的影响。研究结果表明:挤压温度对抗拉强度、屈服强度、粗晶环深度的影响远大于挤压速度和挤压筒温的影响;抗拉强度和屈服强度随挤压温度的升高逐渐升高;粗晶环深度随挤压温度的变化,因是否主动添加Mn元素呈明显的相反趋势变化;过渡族元素Mn、Cr通过影响再结晶过程,影响粗晶环深度;通过有效的挤压温度、速度控制,完全可以使抗拉强度与屈服强度达标,同时粗晶环控制在3 mm以内。     

2A50合金正反挤压棒粗晶的对比

阐述了２Ａ５０合金反挤压棒材粗晶区的分布特征,以及与正抗压棒材粗晶环的差异。通过对该事金正反挤压棒粗晶的试验研究,发现２Ａ５０合金反挤压棒材粗晶区由两部分组成;最外层深度小于２．０ｍｍ的粗大晶粒区和由粗晶区向中心延伸的小晶粒区,这同正坟棒材粗晶环有很大差异。试验结果表明：２Ａ５０合金反挤压棒材边部由粗晶区向中心延伸的小晶粒区是不完全再结晶组织,不应属于粗晶环。     

层片状结构超细晶镍的腐蚀行为

通过动电位极化试验、电化学阻抗试验研究了等通道角挤压制备得到的层片状结构超细晶Ni在3.5%NaCl溶液中的耐腐蚀性,并与退火态粗晶Ni的耐蚀性进行了对比。结果表明,相较于粗晶Ni而言,层片状结构超细晶Ni具有更高的腐蚀电位、更低的腐蚀电流、更稳定的表面钝化膜以及更大的容抗弧直径。     

2A50铝合金挤压棒材尾端粗晶的产生原因及改善措施

利用偏振光、高倍组织和模拟等方式对2A50铝合金反挤压棒材尾部漏斗形缩尾、中心粗晶及正挤压表层粗晶环进行试验研究。结果表明,反挤压时尾端中心粗晶形成的原因是,挤压尾端死区的存在及流动金属受堵头的摩擦和冷却作用而使反挤压后期金属流动不均匀所致;正挤压产生的粗晶环,是由于外层金属变形程度比内层的大受到严重的剪切变形,积累的畸变能高,易发生再结晶并长大,且越靠近尾端越严重。同时,提出了改善缩尾、中心粗晶和粗晶环的措施。     

2618A铝合金棒材粗晶环深度控制方法探究

通过调整2618A铝合金的合金化元素、挤压温度、挤压速度等参数,试验研究2618A铝合金棒材粗晶环深度控制方法,以获得最优工艺参数,保证棒材粗晶环深度达到最小范围,满足产品用户和标准规定的要求。经过对比试验与分析,最终得到通过控制Ti与Zr元素含量以及采用低温、慢速挤压工艺达到控制粗晶环深度的方法。     

铝合金反向挤压中的粗晶组织

铝合金反向挤压过程中,不同的挤压工艺条件对粗晶组织将产生不同的影响。结果表明,通过调整模具工作带长度、控制挤压温度和挤压速度,可以减少粗晶组织的产生。     

化学成分对2024铝合金挤压圆棒粗晶环的影响

试验研究了2024铝合金化学成分对其挤压圆棒粗晶环的影响,探讨了化学成分在粗晶环形成过程中的作用。结果表明,Mn元素是2024铝合金化学成分中对挤压圆棒粗晶环影响最明显的元素之一;在均匀化、挤压和淬火条件不变的情况下,增加Mn元素含量能够减少粗晶环的深度;粗晶环的形成是化学成分不均匀和变形不均匀共同作用的结果。     

固溶条件对7136铝合金挤压型材粗晶环的影响

粗晶环是中高强度铝合金挤压型材常见的组织缺陷之一,揭示铝合金型材的粗晶环形成规律对于制定合理的挤压和热处理制度、进而抑制粗晶环的形成具有重要意义。以7136铝合金挤压型材试样为对象,研究不同固溶条件下试样的粗晶环形成规律,并从再结晶组织和析出相形貌分布特征等方面分析粗晶环的形成原因。结果表明:试样的粗晶环形成最低温度为450℃,且随固溶温度的提高,粗晶环深度逐渐增大;固溶温度470℃保温30 min时粗晶环的深度为63 m。在固溶温度470℃下时,随着保温时间的延长,粗晶环的深度开始增加较快,然后逐渐减慢,60 min后,继续延长保温时间粗晶环深度基本不变。在挤压过程中,试样边部再结晶程度约为心部的两倍,同时,由于边部基体Mg、Zn贫化导致析出相(MgZn2)较少,对晶粒长大的抑制作用较弱,因此,挤压试样在固溶过程中易形成粗晶环。     

高性能精密工业铝型材有效摩擦挤压成形关键技术研究与应用

介绍了对航空航天用高性能精密工业铝型材的要求,提出了减少高性能精密工业铝型材挤压过程产生粗晶环的有效办法。采用理论分析和有限元模拟相结合的研究方法分析了有效摩擦挤压方法的特点,得到了3种不同挤压过程挤压力和挤压筒受力与挤压行程的曲线对比关系;推导出了有效摩擦挤压力的计算公式;建立了挤压筒主动运动和挤压杆同向主动运动的有效摩擦挤压方法,通过实验研究表明有效摩擦挤压方法提高了工业铝型材沿长度方向性能的均匀性,减少甚至消除了工业铝型材表面的粗晶环。以上技术应用在125 MN和60 MN等双动铝挤压生产线上,生产出高性能精密工业铝型材,可应用于航空航天和汽车等行业。     

往复挤压镁合金再结晶组织表征

利用往复挤压在300~360℃细化铸态Mg-6Zn-1Y-1Ce合金组织,研究其组织演变和挤压参数对再结晶组织的影响。结果表明：往复挤压合金横截面边缘存在不均匀环,由靠近筒壁的细晶环和粗晶环组成,其宽度随着挤压温度提高而减小;细晶环是由边缘区域与挤压筒壁摩擦而发生第二轮再结晶所致,粗晶环是由再结晶晶粒长大所致;合金晶粒度由变形速率和温度决定,经340℃挤压合金晶粒最细,平均粒径8.2μm。除边缘外,往复挤压过程中合金在挤压阶段发生一次再结晶,墩粗过程和后续多道次挤压变形都是通过晶界滑移实现。因此,随着挤压道次的增加,保温时间随之延长,晶粒随之被粗化。     

Effect of Cr and Zr on the grain structure of extruded EN AW 6082 alloy

The effects of Cr and Zr addition on the coarse grain surface layer in EN AW 6082 tube extrusions were investigated. The decoration of the tube surfaces and the weld seams with coarse recrystallized grains reflects the strain as well as the temperature gradients that predominate across the section of the tubes during extrusion. The recrystallization resistance provided by Mn does not suffice to avoid the coarse surface grains. With structural features that are almost identical to those of the base 6082 alloy, the 6082 alloy with 0.06 wt% Zr also fails to offer any improvement. The coarse grain surface layer is much thinner and recrystallization is entirely avoided across the weld seams upon the addition of 0.15 wt% Cr. The superior recrystallization resistance of the revised alloy is attributed to the increase in the population of the Cr-rich Al(Cr,Mn,Fe)Si as well as (Al, Si)₃Zr dispersoid particles. It is reasonable to conclude that the coaddition of Zr and Cr has a favourable impact on the resistance to recrystallization of EN AW 6082 alloy.     

线材表面对称粗晶形成原因分析

针对超低碳钢高速线材盘条尾部表面对称粗晶进行了研究,分析了粗晶出现的位置、表面组织形态及相应的生产工艺环节。结果表明：线材表面对称粗晶是由于线材尾部在吐丝前夹送辊夹持时产生微变形,其表面奥氏体晶粒并没有发生动态再结晶晶粒细化,而是在随后的缓慢冷却过程中发生了奥氏体的静态再结晶晶粒粗化,尤其在表层以下的近表面的位置,晶粒以迅速长大的方式向表面变形储存能较高的区域推进,将夹送辊夹持带来的变形能释放,从而造成表面局部奥氏体晶粒异常粗大。为此,改变夹送辊的孔型设计,可解决线材表面对称粗晶问题。     

Effect of Extrusion Profile on Surface Microstructure and Appearance of Aluminum Extrusions with Different Fe Contents

Aluminum alloy extrusions with variations in profiles and Fe-rich particles were produced using different extrusion dies and iron contents. A microstructural examination of the extrusion surface shows that the extrusion profile and iron content have a great effect on the size and number of Fe-rich particles, grain size, texture, and fraction of high-angle grain boundaries due to varying localized plastic deformation and temperature in the extrudate. After etching and anodizing, surface imperfections such as grain boundary grooves that influence the final surface appearance are formed on the extrusion surfaces. The severity of grain boundary grooves is found to be directly linked to the number of Fe-rich particles. Hence, the extrusion profile has a dramatic influence on surface imperfections and the appearance of the final anodized extrusions through its effect on the surface microstructure.     

快速凝固+热挤压制备Al-10.7Zn-2.4Mg-0.9Cu合金的组织和性能

采用单辊熔体旋转法制备Al-10.7Zn-2.4Mg-0.9Cu合金带材,利用热挤压将带材坯料制成棒材,对其微观组织和力学性能进行研究。结果表明:所制备的带材由过饱和固溶体α(Al)等轴细晶构成,晶粒尺寸为3~5μm;合金经挤压后存在粗大第二相,析出相主要为MgZn2相,挤压态棒材抗拉强度为499.8 MPa,伸长率达到了15.3%,断口呈韧性断裂特征;经T6热处理后,合金中有细小的沉淀相析出,使得室温力学性能得到提高,抗拉强度达到631.9 MPa,伸长率有所降低,断口呈韧脆混合断裂特征。     

挤压比对Mg—Zn—Zr—RE合金组织和性能的影响

研究了不同挤压比对铸态Mg-5．4Zn-0．3Zr-0．98RE镁合金微观组织和力学性能的影响。研究表明,当挤压比较小时,微观组织呈现出粗晶和细晶组成的混晶组织;随着挤压比增加到16,微观组织发生完全再结晶,获得均匀、细小的再结晶组织。动态再结晶是铸态镁合金Mg-5．4Zn-0．3Zr-0．98RE晶粒细化的机制。在挤压温度为250℃,挤压比为16时,合金获得的力学性能最好,抗拉强度为345MPa,屈服强度为223MPa,断后伸长率为21．4％。     

Effects of tensile test parameters on the mechanical properties of a bimodal Al–Mg alloy

The properties of aluminum alloy (AA) 5083 are shown to be significantly improved by grain size reduction through cryomilling and the incorporation of unmilled Al particles into the material, creating a bimodal grain size distribution consisting of coarse grains in a nanocrystalline matrix. To provide insight into the mechanical behavior and ultimately facilitate engineering applications, the present study reports on the effects of coarse grain ratio, anisotropy, strain rate and specimen size on the elastic–plastic behavior of bimodal AA 5083 evaluated in uniaxial tension tests using a full-factorial experiment design. To determine the governing failure mechanisms under different testing conditions, the specimens’ failure surfaces were analyzed using optical and electron microscopy. The results of the tests were found to conform to Joshi’s plasticity model. Significant anisotropy effects were observed, in a drastic reduction in strength and ductility, when tension was applied perpendicular (transverse) to the direction of extrusion. These specimens also exhibited a smooth, flat fracture surface morphology with a significantly different surface texture than specimens tested in the axial direction. It was found that decreasing specimen thickness and strain rate served to increase both the strength and ductility of the material. The failure surface morphology was found to differ between specimens of different thicknesses.     

LCAK钢表层粗晶缺陷的产生原因及机理研究

本文研究了LCAK钢热轧带钢表层粗晶缺陷的特征,发现粗晶缺陷组织区域长10～25mm不等,深80～180μm不等,晶粒尺寸可达数百微米。通过对缺陷卷的成分、尺寸规格、生产工艺等因素的对比分析研究,结合本类钢种CCT曲线测定、实验室模拟轧制等手段,详细研究了LCAK钢表层粗晶缺陷产生的原因及材料学机理。结果表明,两相区小变形是导致LCAK钢表层粗晶缺陷的主要原因,该小变形由卷取前夹送辊施加。通过降低夹送辊压力并配合层流冷却的改善,成功控制了表层粗晶缺陷的发生率。     

Microstructure and mechanical properties of Al−Mg−Si alloy U-shaped profile

To get a full understanding of hot extrusion, solid solution treatment and aging process on the Al−0.56Mg− 0.63Si alloy, the microstructure and mechanical properties of a U-shaped profile were studied through optical microscopy, scanning electrical microscopy, transmission electrical microscopy, hardness, and tensile tests. The coarse equiaxed grains existed near the profile edge as a result of the dynamic recrystallization nucleation and exceeding growth during hot extrusion. The fibrous deformed and sub-structured grains located between the two coarse grain layers, due to the occurrence of work-hardening and dynamic recovery. Perpendicular needle β′′ precipitates were distributed inside the grain, and obvious precipitates-free zone appeared after aging treatment. The tensile strength, yield strength and elongation of the aged Al−Mg−Si alloy U-shaped profile were no less than 279.4 MPa, 258.6 MPa, and 21.6%, respectively. The fracture morphology showed dimple rupture characteristics. The precipitates and grain boundaries played key role in the strengthening contribution.