镁合金钨极氩弧焊接头深冷强化机制

针对镁合金焊接接头软化问题,文中提出了AZ31镁合金TIG焊接接头深冷强化方法,进行了镁合金TIG焊接工艺试验和焊接接头的-160℃,8 h深冷处理试验;深冷处理使镁合金焊接接头抗拉强度从212.4 MPa提高到246.6 MPa;用X射线衍射仪(XRD)和透射电子显微镜(TEM)等观测了焊接接头深冷前后的微观组织与结构,分析了焊接接头深冷强化机理.结果表明,深冷处理使镁合金TIG焊接接头形成亚晶结构,第二相Mg17Al12颗粒弥散析出,提高了基体连续性,第二相颗粒数量增加,使接头组织细化并获强化,深冷处理使焊接接头的晶粒发生转动与位错转化为位错环,使接头组织产生孪晶,强化了焊接接头.     

Numerical simulation of deep cryogenic treatment electrode tip temperature for spot welding aluminum alloy

Deep cryogenic treatment technology of electrodes is put forward to improve electrode life of resistance spot welding of aluminum alloy LF2.Deep cryogenic treatment makes electrode life for spot welding aluminum alloy improve.The specific resistivity of the deep cryogenic treatment electrodes is tested and experimental results show that specific resistivity is decreased sharply.The temperature field and the influence of deep cryogenic treatment on the electrode tip temperature during spot welding aluminium alloy is studied by numerical simulation method with the software ANSYS.The axisymmetric finite element model of mechanical,thermal and electrical coupled analysis of spot welding process is developed.The numerical simulation results show that the influence of deep cryogenic treatment on electrode tip temperature is very large.     

深冷处理对铝合金点焊电极烧损的影响

为研究深冷处理对铝合金点焊电极烧损的影响，采用深冷处理和未深冷处理两种铝合金点焊电极进行了点焊工艺试验，观测了两种电极端面宏观形貌和焊点表面宏观形貌。测试了达到未深冷处理电极寿命焊点数时两种电极端面的显微硬度。采用X射线衍射方法对达到未深冷处理电极寿命焊点数时的两种电极端面进行了分析。研究结果表明：在点焊工艺试验过程中，在一定的焊点数条件下，深冷处理电极端面和所焊焊点表面比较光亮、圆整；电极端面的显微硬度较低，并且分布均匀；电极端面未发现烧损后的产物，深冷处理使电极烧损程度显著降低。     

深冷处理提高镀锌钢板点焊电极寿命的机理

为了提高镀锌钢板点焊电极寿命，作者提出了镀锌钢板点焊电极的深冷处理方法。采用不同深冷处理工艺参数处理了点焊镀锌钢板的Cr—Zr—Cu合金电极，用这些电极进行了镀锌钢板点焊电极寿命试验并与未深冷处理的电极寿命进行了比较。用扫描电子显微镜对深冷处理电极进行了背散射及面扫描分析，用X射线衍射法观测了深冷处理前后的电极晶粒度，测试了电极在深冷处理前后的电阻率。通过对深冷电极微观结构的观测及电极性能的测试，探讨了深冷处理提高镀锌钢板点焊电极寿命的机理。研究结果表明，深冷处理提高了镀锌钢板点焊电极基体的致密性，改变了合金元素的分布，细化了电极材料的晶粒，提高了镀锌钢板点焊电极的导电、导热能力及电极抗压渍变形的能力，从而提高了镀锌钢板点焊电极的寿命。     

Effect of deep cryogenic treatment on mechanical behavior of a Cu-Cr-Zr alloy for electrodes of spot welding

The effects of deep cryogenic treatment on mechanical behavior of a Cu-Cr-Zr alloy for electrodes of spot welding were investigated employing Brinell-hardness testing unit, abrasion examination machine, electronic almighty testing machine and X-ray stress analyzer. Tensile fracture surfaces of the alloy were characterized by scanning electronic microscope （SEM） with energy dispersive X-ray spectroscopy （EDS）. The results showed that, after deep cryogenic treatment, σb and σ0.2 increased 23 MPa and 21 MPa respectively, the wear rate of the alloy exhibited the trend of decrease with the decreasing temperature and increasing time of deep cryogenic treatment, and the surface residual stress of the alloy was partially eliminated by deep cryogenic treatment.     

高压扭转变形Mg-Zn-Y合金的组织演化和时效行为

采用透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)仪和显微硬度计研究了高压扭转(HPT)变形Mg-Zn-Y合金的微观组织演变和时效行为.结果表明,在HPT变形前后,合金中的第二相颗粒是W相和Mg24Y5相,且在HPT处理后没有观察到任何新沉淀物的形成,说明HPT变形并未导致合金发生相变.同时,发现HPT变...     

深冷处理对TC4钛合金表面性能的影响

研究了深冷处理对TC4钛合金滚磨光整加工和表面性能的影响。对TC4钛合金试样进行深冷处理,将不同深冷时间下的试样进行滚磨光整加工,根据表面粗糙度确定适合的深冷时间后,对比分析深冷处理前后合金试样的显微组织、显微硬度及残余应力的变化。利用扫描电镜探究了深冷处理和滚磨光整加工后合金试样表面形貌的变化。结果表明,深冷处理12 h后试样表面粗糙度最小,试样组织受到冷缩内应力的作用,α相的比例从未深冷处理的56.45%增加到85.42%,组织变得均匀且致密。试样的显微硬度在深冷处理12 h时最大,比未处理试样提高了3.47%。深冷处理12 h和滚磨光整加工后的试样相比未处理试样表面残余压应力增加26.26%。粗糙度测量和扫描电镜结果显示深冷处理使钛合金试样的可加工性增强,深冷处理12 h的试样经过离心式滚磨光整加工表面粗糙度可从约0.500 μm下降到约0.250 μm,表面质量明显变好。     

电极深冷处理对镀锌钢板点焊质量的影响

采用深冷处理的方法处理了点焊镀锌钢板的电极，进行了电极深冷处理前后的点焊接头强度试验，研究了深冷处理对镀锌钢板点焊接头强度的影响。试验结果表明：电极深冷处理改善了镀锌钢板点焊工艺，提高了点焊接头强度，从而提高了点焊质量。     

深冷处理对K6509钴基合金表面性能的影响

研究了K6509钴基合金样品在-196 ℃液氮中分别深冷24 h和48 h后的表面性能变化,并与未深冷样品进行对比。通过显微组织分析、XRD成分分析、硬度分析等技术手段研究了深冷处理对钴基合金表面性能的影响,并分析了深冷处理和滚磨光整加工后表面粗糙度和形貌的变化。结果表明:钴基合金在深冷处理24 h时,有部分碳化物发生粗化,同时伴随着细小碳化物析出,深冷48 h时细小碳化物减少,碳化物粗化现象消失,显微组织变得均匀;通过XRD图谱发现,深冷过程中相组成没有发生变化,但含M₂₇C₆碳化物的共晶相和含M₇C₃碳化物的共晶相出现峰移现象,M₂₇C₆碳化物相衍射峰强度发生明显变化;延长深冷时间能够显著提高硬度,深冷48 h硬度提高了17.6%;选择合理的深冷时间与滚磨光整加工相结合能显著提高表面质量,经深冷48 h+滚磨光整处理后,表面粗糙度下降最多,R_a由1.215 μm降到0.662 μm,其表面缺陷明显减少,表面一致性好。     

Microstructure evolution during cold rolling in a nanocrystalline Ni–Fe alloy determined by synchrotron X-ray diffraction

Stress softening after cold rolling is observed in an electrodeposited nanocrystalline Ni–Fe alloy. The grain-size distribution becomes much broader after the cold rolling. Microstructure changes, though moderate, such as simultaneously decreased dislocation and twin densities with grain growth during cold rolling, are systematically proved by synchrotron high-energy X-ray diffraction, transmission electron microscopy and differential scanning calorimetry (DSC). The amorphous fractions in the form of grain boundaries are evidenced by the diffuse-background scatterings and large DSC values. Partial dislocation separation calculation, a dislocation mean free path and annihilation model, and texture development together reveal that the current nanocrystalline Ni–Fe alloy exhibits the combined behavior of perfect dislocation slip and grain-boundary mediated deformation.     

均匀化和深冷处理对3104铝合金变形行为的影响(英文)

利用电子万能拉伸试验机、扫描电子显微镜(SEM)、透射电子显微镜(TEM)研究3104铝合金经不同复合热处理制度(深冷处理+均匀化处理)处理后的力学性能和变形特征。先经深冷处理再均匀化处理的试样具有优异的综合力学性能,其抗拉强度、屈服强度和伸长率分别比仅经常规均匀化处理的试样提高了29%、41%和11%。经均匀化处理的试样的应力-应变曲线出现Portevin-Le Chatelier效应,而仅经受深冷处理的试样没有出现Portevin-Le Chatelier效应。这表明先深冷处理再均匀化处理可以促进3104铝合金中第二相弥散析出,大量细小、均匀分布的沉淀相强化了溶质原子对位错的钉扎效应,提高了3104铝合金的临界应变值。     

不完全再结晶Fe40Mn10Cr25Ni25高熵合金的室温及低温力学性能

采用冷轧和退火热处理工艺制备了不完全再结晶结构的Fe₄₀Mn₁₀Cr₂₅Ni₂₅高熵合金,分析了合金的室温(298 K)及低温(77 K)拉伸时的力学性能。结果表明,合金具有优良的室温及低温力学性能,合金在低温拉伸时强度和塑性均得到了提高,其室温强度和断后伸长率分别为880 MPa和18%,低温强度和断后伸长率分别为1360 MPa和36%。合金在室温变形以位错滑移为主,低温变形以位错滑移和孪生为主。室温拉伸时,粗晶晶粒先于细晶晶粒变形,导致试样内部产生了应变梯度,提高了合金的加工硬化率,使合金在室温下具有良好的强塑性。低温拉伸时,粗晶晶粒中形成了大量的变形孪晶,从而提高了合金的低温力学性能。     

Cr12钢深冷处理工艺试验

采用正交试验方法研究了Cr12钢试样的深冷处理工艺,以洛氏硬度、磨损试验及XRD等手段,对不同工艺条件下材料深冷处理前后力学性能和组织进行了对比分析。结果表明,经深冷处理后材料的硬度和耐磨性得到了提高,马氏体衍射峰值增强,衍射峰发生了宽化,马氏体组织细化。根据试验结果提出了合理的深冷工艺。     

Microstructure and Mechanical Behavior of Al 7075-T6 Subjected to Shallow Cryogenic Treatment

The effect of shallow cryogenic treatment (SCT) on the microstructure and mechanical properties of Al7075-T6 is investigated in the present work. The alloy was subjected to shallow CT at ?80 °C for 72 h. Mechanical tests such as Vickers hardness test, tensile, and fatigue tests were performed on both native and treated samples. It was observed that the mechanical properties such as hardness, yield strength, and ultimate tensile strength increased by about 30, 17, and 7%, respectively, for the treated sample. The treated alloy was characterized by using the techniques such as optical microscopy, electron back scattered diffraction (EBSD), energy-dispersive x-ray spectroscopy (EDS), and transmission electron microscopy (TEM) to observe the changes in the microstructural features. EBSD results show precipitation, better distribution of second-phase particles, and higher dislocation density in the treated alloy as compared to the untreated alloy. The treatment imparts improved hardness and strength to the alloy due to precipitation hardening and high dislocation density. Fracture morphologies of the treated and the native samples were characterized by using scanning electron microscopy and it was observed that the striations were denser in the treated sample justifying the higher fatigue strength.     

Microstructural Evolution and Biodegradation Response of Mg-2Zn-0.SNd Alloy During Tensile and Compressive Deformation

The effect of deformation behavior on the in vitro corrosion rate of Mg-2Zn-0.5Nd alloy was investigated experimentally after uniaxial tensile and compressive stress.The microstructure and texture were characterized using electron backscattered diffraction and X-ray diffraction,while potentiodynamic polarization and immersion tests were used to investigate the cor-rosion response after deformation.The result reveals that applied compressive stress has more dominant effect on the corro-sion rate of Mg-2Zn-0.5Nd alloy as compared to tensile stress.Both tensile and compressive strains introduce dislocation slip and deformation twins in the alloy,thereby accelerating the corrosion rate due to the increased stress corrosion related to dislocation slips and deformation twins.The { 10(1)2} tension twinning and prismatic slip were the major contributors to tensile deformation while basal slip,and { 10(1)2} tension twin were obtainable during compressive deformation.The twinning activity after deformation increases with the plastic strain and this correlates with the degradation rate.     

Modification Mechanism and Uniaxial Fatigue Performances of A356.2 Alloy Treated by Al-Sr-La Composite Refinement-Modification Agent

Modification mechanism and uniaxial fatigue properties of A356.2 alloy treated by Al-6Sr-7La and traditional Al-5Ti-1B/Al-10Sr (hereinafter refers to traditional treated alloy) were investigated by constant stress amplitude method. Microstructure, dislocation and Si twinning of the alloys were studied by thermal analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that Al-6Sr-7La possesses better refining and modification effect than Al-5Ti-1B/Al-10Sr. Meanwhile, fatigue properties of the alloy treated by Al-6Sr-7La are higher than traditional treated alloy, and this is mainly owing to that Al-6Sr-7La treated alloy has more twins in eutectic Si and lower twin spacing. In addition, higher density of nanophases formed on twin faces and La-rich clusters appear at multiple twin intersections. Stacking faults and entrapped nanophases appeared on growing Si twin faces. Impurity induced twinning (IIT) mechanism and twin plane re-entrant edge (TPRE) mechanism are valid for eutectic Si which are important for mechanical optimization of A356.2 alloy.     

深冷处理对Al-Zn-Mg-Cu合金在3.5% NaCl溶液中耐腐蚀性的影响

通过深冷处理前后Al-Zn-Mg-Cu合金在3.5%NaCl溶液中腐蚀速率的测试,结合电化学分析及金相和扫描电镜观察,研究了深冷处理对Al-Zn-Mg-Cu合金耐蚀性的影响。结果表明,深冷处理能显著减少Al-Zn-Mg-Cu合金中的第二相含量,从而有效提高Al-Zn-Mg-Cu合金的耐腐蚀性能。     

Exploring the Formation Mechanism of Deformation Twins in CrMnFeCoNi High Entropy Alloy

The deformation twins initiated in CrMnFeCoNi high entropy alloy at cryogenic temperature are experimentally studied. Under the external loading, a three-dimensional shear stress concentration originating from dislocation tangling at both the grain boundaries and twin boundaries could be formed, which promotes emission of partial dislocations from the planar defects and is thus considered to be the key factor for twin formation. A sympathetic nucleation mechanism is proposed to describe the nucleation behaviors of twins.     

轧制对Mg-3Cu-1Mn合金温度阻尼峰的影响(英文)

经过变形量4.7%的单道次室温轧制变形,Mg-3Cu-1Mn合金的一次温度—阻尼谱出现了3个明显的阻尼峰;在二次温度—阻尼谱中,3个阻尼峰均发生变化,特别是第3阻尼峰P3受到抑制,变得非常不明显。对各阻尼峰峰温处淬火样品进行金相、XRD、EBSD等实验,研究轧制对Mg-3Cu-1Mn合金温度—阻尼峰的影响。结果表明:在一次温度—阻尼谱中的P3峰处出现织构增强、孪晶急剧消失的现象;轧制变形后,3个温度—阻尼峰依次为位错阻尼峰、晶界阻尼峰和孪晶引发的再结晶阻尼峰;另外,随着拉伸孪晶的消失,室温轧制态Mg-3Cu-1Mn合金的应变阻尼性能大幅度恢复,高应变下接近均匀化退火态Mg-3Cu-1Mn的应变阻尼性能。这说明拉伸孪晶对Mg-3Cu-1Mn合金应变阻尼性能有不利的影响。     

Effects of compaction pressure on the electrochemical properties of Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 metal hydride electrodes

In this work, the negative electrodes of the nickel-metal hydride rechargeable batteries were prepared at different compaction pressures. The maximum discharge capacities and cycle stabilities of the electrodes were measured by means of electrochemical method. The crystal structures and surface morphologies of the alloys were intensively studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS), respectively. Based on these observations, the effects of compaction pressure on the electrochemical properties of the electrodes were systematically investigated. The results showed that the electrode prepared at a compaction pressure of 25 MPa exhibited the best discharge capacity and better cycle stability.