Al—6Mg合金超塑性变形与空洞的研究

本文研究了Al—6Mg合金超塑性拉伸变形中的力学特性和显微组织的变化。试验结果表明,合金在520℃以ε=8.33×10~(-4)S~(-1)的应变速率拉伸,得最高延伸率578%,流动应力为1.6MN/m~2,m=0.68,合金通过静态再结晶得到等轴晶粒(11μm)。并对空洞生核和扩展,空洞与变形机制、廷伸率以及断裂进行了探讨。     

Al-5.5Zn-2.5Mg高强铝合金微观组织与疲劳性能

通过光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)等方法观察了Al-5.5Zn-2.5Mg高强铝合金材料的微观组织,并进行了拉伸性能与疲劳性能试验,分析其拉伸断裂和低周疲劳失效行为.结果表明:Al-5.5Zn-2.5Mg高强铝合金的力学性能与低周疲劳性能较好,拉伸强度达到479.4 MPa.当应力比R=-1,频率f=20 Hz,应变幅εa=0.8％时,低周疲劳寿命为630周,疲劳裂纹萌生于试件表面,且疲劳裂纹扩展区存在明显的疲劳条带.Al-5.5Zn-2.5Mg铝合金η’(MgZn2)析出相虽然在光学组织中呈现均匀弥散分布,但在TEM高倍组织中主要沿晶界析出,强化相粒子的平均直径约20 nm,晶界附近无沉淀析出带宽约100 nm.     

LF6铝合金超塑变形机理的研究

借助于高放大倍率的二次复型组织，观察了ＬＦ６铝合金超塑变形后的表面晶粒组织。对目前公认的晶界滑动（ＧＢＳ）、扩散蠕变（ＤＣ）、位错滑移（ＤＳ）三种变形机理在不同应变速率下变形时各自所占的比例进行了测定和计算。根据计算结果，讨论了三种变形机理在变形过程中的相互作用和协调关系。     

Microstructural characterization and mechanical property of Fly Ash/Al-25Mg composites

Fly ash/Al-Mg composites are fabricated by powder metallurgical method. The morphology and structure of fly ash/A l-Mg composites are characterized by scanning electron microscope （SEM） and X-ray diffraction, respectively. The influences of different fly ash content on the friction and wear behavior of the composites are investigated at a constant sliding velocity of 400 r/min and the worn mechanism of composites is discussed. The results indicate that the friction coefficient is steadily lower than that of Al alloy matrix at the lower fly ash content and loads. For the fly ash/Al-Mg composites, the wear mechanism is characterized as abrasive wear and adhesive wear under small normal load and at low fly ash content, and it is characterized as delamination wear and abrasive wear transferred onto the counterpart under high normal load and at high fly ash content.     

Temperature Field and Microstructural Formation of Semi-Solid AlSi7Mg Alloy

The microstructural formation of the semi-solid AlSi7Mg alloy stirred by electromagnetic field is investigated together withthe tempeatre field of the stirred melt at continuously cooling. A impoat kinetic factor for primny a-Al nucleation is proposed. It isfound that a low temperatUre gradient exists in the electromagnetic stirred melt. This is why the first dendritic arms and secondary de-ndritic arms are refmed. Experimefltal results also show that the root remelting of secontw dendritic arms is an twortat mechanismfor the primary α-Al refmement. Strong electromagnetic stirring greatly reduces the composition supercooling in the melt and eliminatesprefedrig growth of the first dendritic arms. Therefore, many rosettes or spherical Primary α-Al phase particles form finally.     

Microstructural Characteristics of CuCr50 Alloy by Laser Refining

An investigation conceming the thecrostructural characterization of CuCr50 alloy layer by laser surface refining on the powder metallurgy substrate was carried out Significant refined procutectic chromium crystals distributed in an Cr-rich eutectic and high mutual solubility of Cu and Cr elements in the CuCr50 alloy were exam ined by Backscattered Eectron Imaging (BEI) and Energy Dispersive X-ray Spectrum (EDS) techniques. The results show that surface refining and alloying by high-power laser have a great potential to develop new and high performance alloys in the immiscible and limited solubility systems like Cu-Cr and other similar alloy systems.     

脉冲电流对Zn－22Al合金超塑性力学行为的影响

本文以普通处理的Ｚｎ－２２Ａｌ合金板坯为对象，研究了脉冲电流对其超塑性力学行为的影响．实验结果表明：在脉冲电流作用下，合金的延伸率和应变速度敏感性指数有了很大提高，流动应力降低．在高应变速率（３．３×１０（－２）ｓ（－１））下，该合金仍具有很高的延伸率．最佳超塑变形温度向低温度方向偏移．合金的超塑变形可在更低温度下进行．     

复合中间合金对铝合金机械性能的影响

以工业纯铝（L2）为基础,添加不同百分含量的合金元素Re、Al-Ti-B与Al-X等,以及选择适当的热处理工艺措施,对其所引起的机械性能、导电性能的变化进行了研究,旨在寻求一种新的复合中间合金材料替代原来各合金元素单独加入,从而获得导电性较好,强度较高的铝合金电脑散热片材料．研究结果表明：当加入的复合中间合金中Re、Al-Ti-B与Al-X比例为1：3：1时,其效果最佳．     

5083-H321铝合金板材搅拌摩擦焊缝组织演变

采用搅拌摩擦焊接法焊接了5083-H321铝合金板材,借助光学显微镜、扫描电镜、背散射电子衍射分析仪及取向显微成像分析技术对焊缝与母材的组织进行了对比性研究.结果表明,该合金板材的焊缝无宏观缺陷,焊缝成形区呈现出与母材明显不同的组织特征;搅拌摩擦焊使该合金板材中大量的小角度晶界转化为大角度晶界,母材和焊核区的晶粒尺寸分布范围分别为6-55 μm及15-30 μm,晶粒纵横比分布范围分别为2~8和15-3,焊核区呈现均匀化与等轴化的动态再结晶特征.     

EDTA络合滴定法快速测定铝合金中的镁

与通常采用的测定方法不同的是测定过程中，不使用氰化钾，避免了对人和环境的污染．     

Al-0.6Mg-0.6Si铝合金MIG焊接接头显微组织与微区成分研究

对轨道车辆用新型Al-0.6Mg-0.6Si铝合金进行了熔化极隋性气体保护(MIG)焊接,利用光学金相(OM)、能谱(EDAX)分析等测试手段,对焊接接头的显微组织与微区成分(质量分数)进行 了分析.结果表明:采用MIG焊接方法能够获得成形良好的接头,焊缝中心结晶形成典型铸态组织,但易于偏聚形成显微夹杂,靠近熔合线的焊缝逐渐由焊缝边缘的柱状晶过渡到枝状晶.熔合线附近的焊缝边缘易于形成Si偏析带,A1-0.6Mg -0.6Si基体组织的质量比m(Mg):m(Si)≈1.04:1,焊缝中心Mg元素受电孤高温烧损,Mg含量(质量分数)为3.08％.     

Al—Zn—Mg—Cu合金的超塑性变形力学行为

介绍了一种新的超塑性处理工艺,采用简单的预处理工艺结合升温拉伸,可以使合金获得优异的超塑性,轧制形变组织在拉伸过程中发生动态再结晶,形成细晶组织并赋予合金优异的超塑性。     

熔体热历史对Al-11.6%Si合金组织及性能的影响

本文研究了熔体加热温度和保温时间对Al-11.6%Si合金显微组织及性能的影响.研究发现,合金液的加热温度和保温时间不仅影响合金凝固的组织,而且也影响其力学性能.将合金液温度从720℃升到900℃,共晶硅由粗大的针片状变为点状或短棒状、合金抗拉强度提高了6.33%、延伸率提高了10.83%.升温后的保温时间对合金组织和力学性能的影响时间不同于降温后的保温时间,随升温后保温时间的延长,合金的组织变细、抗拉强度和延伸率提高;随降温后保温时间的延长,合金的组织变粗、抗拉强度和延伸率降低.     

Microstructural,Mechanical,Electrical,and Thermal Properties of the Bi-Sn-Ag Ternary Eutectic Alloy

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries.Bi-Sn-Ag eutectic alloy has been considered as one of the lead-free solder materials that can replace the toxic Pb-Sn eutectic solder without increasing soldering temperature.We investigated the effects of temperature gradient and growth rate on the mechanical,electrical and thermal properties of the BiSn-Ag ternary eutectic alloy.Bi-47 wt%Sn-0.68 wt%Ag alloy was directionally solidified upward with different temperature gradients(G=2.33-5.66 K/mm) at a constant growth rate(V=13.25 μm/s) and with different growth rates(V=6.55-132.83 μm/s) at a constant temperature gradient(G=2.33 K/mm) in the growth apparatus.The microstructures(λ),microhardness(HV),tensile stress(σ),electrical resistivity(ρ),and thermal properties(△H,C_p,T_m) were measured on directionally solidified samples.The dependency of the λ,HV,σ,and ρ on G and V was investigated.According to the experimental results,X values decrease with increasing G and V,but HV,λ,and ρ values increase with increasing G and V.Variations of electrical resistivity(ρ) for cast samples with the temperature in the range of 300-400 K were also measured by using a standard dc four-point probe technique.The enthalpy of fusion(△H) and specific heat(C_p) for the same alloy was also determined by means of differential scanning calorimeter(DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.     

时效时间对新型高强铸造Al-Cu-Mn合金性能和微观组织的影响

本文研究了Al-Cu-Mn铸造铝合金在（540±5）°C保温14h固溶处理后,在175℃下时效时间对其强度、塑性和微观组织结构的影响。研究结果表明：Al-Cu-Mn铸造合金获得较高的拉伸强度（σb﹥455Mpa）和较好的延伸率（δ﹥8%）的时效时间范围是3～8小时,其中5小时时效的拉伸强度σb达到最高480MPa,对应的延伸率为8.2%。时效时间对试样的拉伸强度影响不大,其原因在于强化方式主要以时效沉淀相θ′和二次T相的弥散强化为主。材料的延伸率随着时效时间的延长而下降,时间大于10小时后,延伸率明显下降（<5.0%）,其原因在于时效时间过长,导致了晶界沉淀相从链条状分布变为粗大块状,晶界无析出带过宽,二次T相偏聚严重,晶内出现明显的空白区域,以及晶界呈网状割裂基体等微观组织结构。这些因素的综合作用使得Al-Cu-Mn试样的塑性下降。     

Microstructure and Mechanical Properties of Friction Stir Welded 7050-T7451 Aluminum Alloy Plates

7050-T7451 aluminum alloy plates was friction stir welded at different welding parameters.Mechanical properties of the joints were estimated according to tensile test and hardness test.The microstructure evolution during friction stir welding(FSW) was examined using optical microscope(OM) and transmission electron microscope(TEM).The nugget zone(NZ) has a recrystallized,fine equiaxed grain structure with high dislocation density.Strengthening precipitates appear to have gone to solution.Heat mechanical affected zone(TMAZ) was characterized by a highly bend deformed grain structure with partly dynamic recovery and dynamic recrystallization.The grain structure in heat affected zone(HAZ)is similar to that of the base metal with little growth in size and contained a relatively low dislocation density.Strengthening precipitates coarsen severely and the precipitated-free zone(PFZ) along the grain boundaries increase in width.The mechanical properties of the joints were affected by welding parameters with different microstructure and welding defects.The joint with largest tensile strength was welded at the parameters with tool traverse speed of 200 mm/min and rotation rate of 800 r/min,up to 88% of that of base metal.     

高强韧铸造铝合金组织与性能研究

采用正交试验研究了Cu,Mg,Mn,Zn四种元素对新型高强韧耐热Al-Si-Cu-Mg-Mn-Zn合金室温及250℃力学性能的影响规律,分析了Al-7.0Si-2.5Cu-0.5Mg-0.3Mn-0.8Zn合金铸态及热处理后试样的金相显微组织和250℃断口形貌.结果表明:Cu,Mg,Mn,Zn四种元素对Al-Si-Cu-Mg-Mn-Zn合金室温及250℃抗拉强度和延伸率的影响顺序为,Mg>Cu>Zn≥Mn,Mg和Cu是主要影响因素,Mn和Zn是次要影响因素.随着Mg含量的增加,合金室温及250℃抗拉强度升高而伸长率下降,随着Cu含量的增加,合金室温抗拉强度升高而伸长率下降,250℃抗拉强度升高而伸长率呈先升后降趋势,Zn含量的提高有利于提高合金250℃延伸率.为使合金具有良好的综合力学性能(室温及250℃),Al-Si-Cu-Mg-Mn-Zn合金的最佳质量分数为7.0%Si,2.5%Cu,0.3%Mg,0.3%Mn,0.8%Zn,且合金力学性能室温时bσ≥345 MPa,5δ≥6.0%,250℃时bσ≥220 MPa,5δ≥9.0%.     

高速列车用高强铝合金疲劳断口的特征

通过宏观拍照和扫描电镜对A7N01高强铝合金T型焊接接头的疲劳断口进行了研究,揭示了该铝合金疲劳裂纹萌生与扩展的特征.铝合金的疲劳断口可明显划分为疲劳裂纹源区、裂纹稳定扩展区和瞬断区3大区域.疲劳裂纹从T型焊接接头的焊趾处萌生并向接头中心线扩展,疲劳裂纹扩展区可以观察到疲劳破坏的一些典型特征,瞬断区的断口形貌与拉伸断裂相似,形成不平坦的粗糙表面.     

Interfacial Microstructure and Mechanical Properties of Al Alloy/Mg Alloy Laminated Composite Plates Fabricated by Equal Channel Angular Processing

KAl(7075)alloy/Mg(AZ31)alloy laminated composite plates were successfully fabricated by the equalchannelangular processing(ECAP)by using route A for 1,2,and 3 passes at 573 K,respectively.After fabrication,the 1-pass ECAPed laminated composite plates were annealed at different temperatures.The microstructure evolution,phase constituent,and bonding strength near the joining interface of Al(7075)alloy/Mg(AZ31)alloy laminated composites plates were evaluated with scanning electron microscopy,X-ray diffraction,and shear tests.The experimentalresults indicated that a 20 μm diffusion layer was observed at the joining interface of Al(7075)alloy/Mg(AZ31)alloy laminated composites plates fabricated by the 1-pass ECAP,which mainly included Al_3Mg_2 and Mg_(17)Al_(12) phases.With the increase of passes,the increase of diffusion layer thickness was not obvious and the form of crack in these processes led to the decrease of bonding strength.For 1-pass ECAPed composites,the thickness of diffusion layer remained unchanged after annealed at 473 K,while the bonding strength reached its maximum value 29.12 MPa.However,after elevating heat treatment temperature to 573 K,the thickness of diffusion layer increased rapidly,and thus the bonding strength decreased.     

双级均匀化对7055铝合金微结构与力学性能的影响

采用光学显微镜、透射电镜观察、硬度及单向拉伸测试,研究了双级均匀化制度对7055合金微结构与性能的影响。结果表明:与单级均匀化相比,双级均匀化处理的初级低温保温过程有利于原始晶界附近低Zr区域的Al3Zr弥散析出;双级均匀化处理后无沉淀析出带(PFZ)变窄,晶界附近Al3Zr粒子密度增加;弥散分布的Al3Zr粒子通过钉扎晶界与拖曳位错,有效地抑制了再结晶,以至于经热轧固溶后再结晶百分数降低40%左右;保留下来的大量位错和未再结晶组织,提高了合金T6态力学性能。