Effects of Ultrasonic Vibration on Material Flow and Thermal Cycles in Friction Stir Welding of Dissimilar Al/Mg Alloys

Comparative experiments are performed in friction stir welding (FSW) of dissimilar Al/Mg alloys with and without assistance of ultrasonic vibration. Metallographic characterization of the welds at transverse cross sections reveals that ultrasonic vibration induces differences in plastic material flow in two conditions. In FSW, the plastic material in the peripheral area of shoulder-affected zone (SAZ) tends to flow downward because of the weakening of the driving force of the shoulder, and a plastic material insulation layer is formed at the SAZ edge. When ultrasonic vibration is exerted, the stirred zone is divided into the inner and outer shear layers, the downward material flow trend of the inner shear layer disappears and tends to flow upward, and the onion-ring structure caused by the swirl motion is avoided in the pin-affected zone. By improving the flow behavior of plastic materials in the stirred zone, ultrasonic vibration reduces the heat generation, accelerates the heat dissipation in nugget zone and changes the thermal cycles, thus inhibiting the formation of intermetallic compound layers.

     

Mold-filling characteristics of AZ91 magnesium alloy in the low-pressure expendable pattern casting process

The magnesium (Mg) alloy low-pressure expendable pattern casting (EPC) process is a newly developed casting technique combining the advantages of both EPC and low-pressure casting. In this article, metal filling and the effect of the flow quantity of inert gas on the filling rate in the low-pressure EPC process are investigated. The results showed that the molten Mg alloy filled the mold cavity with a convex front laminar flow and the metal-filling rate increased significantly with increasing flow quantity when flow quantity was below a critical value. However, once the flow quantity exceeded a critical value, the filling rate increased slightly. The influence of the flow quantity of inert gas on melt-filling rate reveals that the mold fill is controlled by flow quantity for a lower filling rate, and, subsequently, controlled by the evaporation of polystyrene and the evaporation products for higher metal velocity. Meanwhile, the experimental results showed that the melt-filling rate significantly affected the flow profile, and the filling procedure for the Mg alloy in the low-pressure EPC process. A slower melt-filling rate could lead to misrun defects, whereas a higher filling rate results in folds, blisters, and porosity. The optimized filling rate with Mg alloy casting is 140 to 170 mm/s in low-pressure EPC.     

甲醇合成塔用 150 mm SA387Gr22C12 钢板组织和力学性能

对 150 mm 厚 SA387Gr22C12 钢板( / % : 0．13 ～0．14C,0．09Si,0．55 ～0．56Mn,0．004P,0．001S,2．48 ～2． 49Cr,1．11～1．12Mo) 模拟焊后拉伸性能、－29 ℃ 冲击性能、金相组织及回火脆化倾向评定等进行试验,并检测了交货态(正火 + 回火) 、最小模拟焊后态、最大模拟焊后态及步冷试验后的钢板各项性能指标 。结果表明,钢板的回火脆化 倾向不明显,其结果 CvTr55 + 2．5ΔCvTr55 为－63 ℃,完全满足甲醇合成塔用钢板的技术要求。     

非晶金属丝的电磁性能及其在传感技术中的应用

非晶金属丝具有高的机械强度和优异的电磁特性。利用这些性能，可以用它制作各种传感器件。尤其，Ｆｅ基非晶丝存在大的巴克豪森和迈悌欧斯效应，是无颤动尖锐脉冲电动势发生器件材料。Ｃｏ－Ｆｅ基非晶丝具有零磁致伸缩效应。两类非晶金属丝主要被应用到制作传感器方面。非晶金属丝以它的圆截面形状，可高度集成的优点正在引进电子仪表进行的兴趣。     

Zr替代Ti对Ti19．5V40Mn16．2Cr9．8Ni14．5合金的影响Ⅱ：电化学性能

在对合金微观结构和储氢性能研究的基础上，详细考察了少量Zr取代Ti对Ti19．5V40Mn16．2Cr9．8Ni14．5合金电化学性能的影响。通过观察电极的充放电行为，并结合EIS及多种极化曲线的分析结果，发现少量Zr对Ti的取代能够显著提高合金电极的实际电化学容量和循环稳定性，而且还能在一定程度上改善合金的电极动力学性能。对于这些性能的改善，从合金微观结构方面进行了解释。     

热爆合成－热挤压TiNi棒材的组织结构和性能

研究了热爆合成－热挤压法制得的ＴｉＮｉ合金棒材的组织结构和性能。研究结果表明，所制取的棒材具有用传统法——熔铸法生产ＴｉＮｉ合金的性能，证明了用该法制取ＴｉＮｉ型材的途径是可行的     

低熔点Cu-P基中间合金及其变质效果

利用差示扫描量热仪(DSC)、扫描电子显微镜(SEM)和金相显微镜等手段对Cu-P基中间合金进行了研究。结果表明，在二元共晶Cu-P中间合金中加入一定量的Sn可制成低熔点的Cu-16Sn-8P中间合金；在此基础上研制出一种熔点为630℃左右的低熔点的多元Cu-P基中间合金。与Cu-P中间合金相比，该低熔点多元Cu-P基中间合金对过共晶AI-24Si合金具有更好的变质效果。同时，该中间合金对ZL109合金也具有良好的变质效果。     

（LPCCa）2（MgNi）17合金的吸放氢性能

研究了用部分Ca取代LPC（LPC为无钕镧镨铈混合稀土金属），同时用部分Ni取代Mg的（LPCCa）2（MgNi）17合金的吸放氢性能。比较了不同温度下，不同成分配比对合金贮氢性能的影响。其中，（LPC）1.9Ca0.1Mg15Ni2合金具有相对较低的放氢温度和较大的放氢节，住275℃的放氢量达3．43％（质量分数）。分析了（LPC）1.9Ca0.1Mg15Ni2的微观结构，同时对合金放氢温度降低的原冈进行了讨论。