汽车用铝合金激光填丝焊接工艺

采用激光焊接方法,通过添加5087焊丝实现高强铝合金7075的焊接。结果表明,铝合金激光焊接接头裂纹数量随着激光功率和焊接速度增加而增加,随着填丝速度增加而减小。最佳工艺参数为:激光功率2.5 k W,焊接速度2 m/s,填丝速度2 m/s。激光功率过小或填丝速度过大时,铝合金接头表面成形性差。激光功率越高,或焊接速度越慢,接头焊缝晶粒尺寸越大。     

6005A-T5与7N01-T4异种铝合金搅拌摩擦焊接接头组织与力学性能

采用搅拌摩擦焊(FSW)焊接6005A-T5与7N01-T4铝合金板材,对焊接接头的组织和力学性能进行了研究,探讨板材设置和焊接速度对异种接头材料流动性、组织和力学性能的影响。结果表明:当6005A-T5铝合金位于前进侧(AS)时,材料的混合更加充分,这与6005A-T5铝合金较好的流动性有关。此外,降低焊接速度可以促进材料的混合。焊核区晶粒尺寸随焊接速度的增加而减小。焊接接头的最小硬度均位于6005A-T5铝合金侧热影响区(HAZ),此处为所有接头的拉伸失效位置。随着焊接速度的增加,接头抗拉强度增大,但板材设置对抗拉强度的影响可以忽略不计。     

汽车用7075铝合金搅拌摩擦焊工艺与性能

采用搅拌摩擦焊实现了7050铝合金的焊接,通过金相显微镜、扫描电镜和万能试验机研究了焊接接头组织和性能。结果表明,铝合金搅拌摩擦焊接时,在相同焊接速度下,随着旋转速度的增加,熔核底部未焊透区域增加,熔核区平均晶粒尺寸增加。随着旋转速度与焊接速度比值增加,铝合金搅拌摩擦焊接头抗拉强度降低。焊接速度20 mm/min-1,旋转速度200 mm/min-1时,接头抗拉强度达到最大值373 MPa。固溶处理后铝合金抗拉强度增加。     

高锌铝合金搅拌摩擦焊接头组织和性能

采用不同焊接工艺参数对6 mm厚稀土Er微合金化的高Zn铝合金进行了搅拌摩擦焊试验,研究了不同焊接速度对焊缝各区域组织和力学性能的影响。结果表明:焊核区晶粒尺寸随焊接速度的增加而逐渐减小;热影响区和热机影响区交界处硬度值最低,是焊接接头的薄弱环节。焊接接头存在异常的大梯度组织变化,在三种焊接速度下获得的焊接接头强度损失均较为严重,当搅拌头转速为350 r/min、焊接速度为50 mm/min时,抗拉强度和伸长率分别为459 MPa和9.4%,伸长率比母材横向增加96%,断口分析表明为韧性断裂。     

PLC控制激光焊接2524铝合金接头的组织研究

采用PLC控制激光焊接工艺参数对2524铝合金进行了焊接处理,研究了激光功率、焊接速度和送丝速度对2524铝合金焊接接头热裂纹倾向和显微组织的影响。结果表明,随着激光功率的增加,焊接接头的裂纹总数量呈现不断增加的趋势;焊缝中心为等轴树枝晶组织,而靠近熔合线附近为柱状晶组织,焊缝中心的平均晶粒尺寸和靠近熔合线附近的焊缝柱状晶间距均增大;随着焊接速度的增加,焊接接头的裂纹总数量不断增加,热裂纹倾向加大,且焊缝区域的熔宽和焊缝面积减小;随着送丝速度的增加,焊接接头的裂纹总数量降低。采用填充焊丝的焊接工艺后,焊缝的成形性相对自熔焊接更好,且焊缝面积明显增大。     

5052铝合金激光焊接接头组织和性能研究

采用扫描电镜、显微硬度和抗拉强度等测试方法,研究了5052铝合金激光焊接接头组织和性能。研究结果表明,铝合金激光焊接接头热影响区主要为树枝晶,晶粒较为粗大;焊缝区主要为等轴晶,晶粒较母材和热影响区细小。铝合金激光焊接接头显微硬度焊缝区最高,热影响区最低。随着激光功率的增加,铝合金激光焊接接头抗拉强度先增加后降低,激光功率3.0 k W时达到最大值204.5 MPa,拉伸断口为典型的韧窝断口形貌。     

AZ91D镁合金/Q345钢MIG焊对接接头组织与力学性能研究

采用熔化极惰性气体保护电弧焊(MIG)方法对AZ91D合金/Q345钢异种金属进行了焊接,研究了焊接电流和焊接速度对接头显微组织和抗拉强度的影响。结果表明在不同的焊接电流和焊接速度下焊缝区都为α-Mg等轴晶,AZ91D侧熔合区组织为晶粒尺寸不均的α-Mg晶粒,整体晶粒尺寸较为细小,而热影响区的晶粒尺寸较为粗大。在AZ91D/Q345接头连接处形成一定厚度的过渡层。随着焊接电流的增加,焊接接头晶粒尺寸逐渐增大,抗拉强度呈现先增加而后略降低的趋势;随着焊接速度的增加,焊接接头晶粒尺寸减小,异种金属焊接接头的抗拉强度也呈现先略增加而后降低的特征。     

异种铝合金搅拌摩擦焊接头的显微组织、力学及腐蚀性能

采用3种焊接速度(60、100和240 mm/min)对5 mm厚2024和7075铝合金板材进行搅拌摩擦对接焊试验,利用电子背散射衍射(EBSD)、硬度测试、拉伸试验、扫描电镜和极化曲线测试对2024-7075异种铝合金搅拌摩擦焊接头的显微组织、力学性能及腐蚀行为进行了研究。结果表明:接头焊核区发生动态再结晶形成细小的等轴晶。沿板厚方向从轴肩区到底部区的平均晶粒尺寸依次减小,且焊核区不同位置处的平均晶粒尺寸均随着焊接速度的增加而减小。异种接头焊核区不同位置形成不同类型的剪切织构,其类型随焊接速度的改变而变化。接头焊核区硬度呈现"W"型分布趋势,且低于母材硬度。较低硬度值区域位于热影响区,随着焊接速度的降低,各区硬度值呈现下降的趋势。接头强度随着焊接速度的增加而升高,焊接效率达到90.3%。与母材相比,焊接接头焊核区的耐蚀性最差,这主要是由于异种焊接接头焊核区发生了显著的电偶腐蚀,导致较高的腐蚀电流密度。     

6061铝合金光纤激光填丝焊工艺与性能研究

采用光纤激光填丝焊工艺对6061铝合金进行焊接,研究了激光功率、焊接速度和送丝速度对铝合金激光焊接接头质量和热输入对接头拉伸性能的影响。结果表明,6061铝合金激光填丝最佳焊接工艺为激光功率2 k W、焊接速度3 m/min、送丝速度1.5~3.0 m/min。激光焊接接头抗拉强度随热输入增加而降低,热输入由80 J/mm增加到146J/mm,抗拉强度由218 MPa降低到206 MPa。     

6063铝合金电池盒下壳体搅拌摩擦焊工艺试验研究

试验研究了在较高的焊接速度和搅拌头的旋转速度下,6063铝合金电池盒下壳体焊接接头的力学性能和金相组织。结果表明,在高焊接速度和高旋转速度的搭配下得到的焊接接头强度可以达到母材强度的70%以上,但是部分情况下其伸长率低于母材的。焊接速度和旋转速度的改变对焊接接头强度的影响较小,但是对伸长率的影响较大。焊接速度为800 mm/min时,旋转速度设置到1 500 r/min以上可得到晶粒分明的组织,旋转速度增大会增大晶粒尺寸;搅拌头的旋转速度为1 500 r/min时,焊接速度的增加会逐渐使接头的晶界不清晰;若提升焊接速度的同时也提升旋转速度,则又可得到晶界分明的组织。     

Fabrication of Ti-Cu-Ni-Al amorphous alloys by mechanical alloying and mechanical milling

Ti-based amorphous alloy powders were synthesized by the mechanical alloying (MA) of pure elements and the mechanical milling (MM) of intermetallic compounds. The amorphous alloy powders were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Scanning electron micrographs revealed that the vein morphology of these alloy powders shows deformation during the milling. The energy-dispersive X-ray spectral maps confirm that each constituent is uniformly dispersed, including Fe and Cr. The XRD and DSC results showed that the milling time required for amorphization for the MA of pure elements was longer than that of the MM for intermetallic compounds. The activation energy and crystallization temperature of the MA powder are different from those of the MM powder.     

机械合金化制备Cu-0.5Wt%Nb合金组织与性能的研究

采用机械合金化法制备了Cu-0.5wt％Nb纳米弥散强化铜合金。通过金相、透射电镜观察了该合金粉末态、冷轧态及不同温度退火后合金的组织结构变化。通过测量该合金不同状态的硬度及相对电导率,实验结果表明,其冷轧态硬度较高(可达160kg/mm2),随退火温度升高硬度呈缓慢下降趋势;900℃退火后,硬度仍可达91kg/mm2,表明此合金抗高温软化性能较好.此外该合金相对电导率最高可达89% IACS,这进一步说明利用机械合金化法制备的Cu-0.5wt%Nb合金具有优越的综合性能.     

Optimization of a double knuckle linkage drive with contrast mechanical advantage for mechanical presses

Mechanical presses are widely used in the metal-forming industry because they are inexpensive, easy to automate, need low maintenance and offer high production rates. This paper is Part I of a three part series on the development of a flexible computer controlled precision press with double-toggle linkage driven by a servo-motor. It discusses techniques for simulating the load-stroke characteristics of mechanical linkage drives and presents results of comparison of a newly developed double-toggle linkage drive with four example drives from commercial metal-forming presses. The paper concludes that though this new design has lower mechanical advantage than some of these commercial drives, its ability to deliver constant load over most of the stroke makes it a strong competitor to hydraulic presses in the extrusion and sheet metalforming applications. In addition the drive, developed in this study, is found to be efficient in terms of space requirements.     

机械超材料研究进展

机械超材料因其具有与直觉相悖的力学性能而受到学者的广泛关注。其独特新颖的性能与自身结构紧密相关,通过设计和制备不同的结构,能够使材料具有许多独特的力学性能。目前,制备工艺的发展和进步使得制备具有任意复杂微米或纳米结构的材料成为现实。本文综述了机械超材料领域中较为常见的几种性能：轻质超强、负泊松比、负可压缩性、负热膨胀性和超流体的研究进展,总结了机械超材料发展的限制因素,并对该领域的发展方向及研究重点进行了展望。     

Mechanism of mechanical press joining

Mechanical press joining has been studied for many years in the hope of achieving quality joints for dissimilar sheet metals or materials with different surfaces and thicknesses. In most of the manufacturing practices involved, the workpieces are first cut or drawn by proper punching. Then, the workpieces are clamped together by an impact extrusion between a punch and a female die. This process has been a recent resurgence in the field of permanently fastening precoated or dissimilar sheet metals, sandwich panels made of plastic and metal and pre-formed sheet metal assemblies with screws and nuts. This paper is concerned with the basic mechanism of mechanical press joining, which is useful for designing such joining elements. Some basic terms, such as the mechanical contact chains and their symbols and the joint networks, are introduced to establish a basic theory for analyzing the joining mechanism. Using joint networks consisting of the symbols of contact chains an efficient design method is presented. Some widely used mechanical press joining elements are discussed in detail in view of their mechanical behavior.     

Atomistic modeling of mechanical behavior

Atomistic modeling plays a critical role in advancing our understanding of microstructure evolution and mechanical properties. We present progresses in the theory and computation of ideal strength, dislocations activation processes and brittle fracture from the atomic perspective, in close connection with experiments and other levels of modeling. New discoveries are often made in the “virtual atoms labs”. There, one has perfect control of the simulation conditions, and the amount of detailed atomistic information is often breathtaking. Yet, this information can only be seen, utilized and appreciated in full in light of experiments and models for other length/time-scales.     

Microstructure evolution and mechanical properties of nanocrystalline FeAl obtained by mechanical alloying and cold consolidation

In the present study high energy mechanical milling followed by cold temperature pressing consolidation has been used to obtain bulk nanocrystalline FeAl alloy. Fully dense disks with homogenous microstructure were obtained and bulk material show grain size of 40 nm. Thermal stability of the bulk material is studied by XRD and DSC techniques. Subsequent annealing at a temperature up to 480 °C for 2 h of the consolidated samples enabled supersaturated Fe(Al) solid solution to precipitate out fine metastable Al₅Fe₂, Al₁₃Fe₄ and Fe₃Al intermetallic phases. Low temperature annealing is responsible for the relaxation of the disordered structure by removing defects initially introduced by severe plastic deformation. Microhardness shows an increase with grain size reduction, as expected from Hall-Petch relationship at least down to a grain size of 74 nm, then a decrease at smallest grain sizes. This could be an indication of some softening for finest nanocrystallites. The peak hardening for the bulk nanocrystalline FeAl is detected after isochronal ageing at 480 °C.