Fabrication of robust aluminum–carbon nanotube composites using ultrasonic assembly and rolling process

This study introduced a novel fabrication of aluminum–carbon nanotube(CNT) composites by employing bulk acoustic waves and accumulative roll bonding(ARB).In this method, CNT particles were aligned using ultrasonic standing wave in an aqueous media, and the arrayed particles were precipitated on the aluminum plate substrate.Then, the plates rolled on each other through the ARB process with four passes.Optical and scanning electron micrographs demonstrated the effective aligning of CNTs on the aluminum substrate with a negligible deviation of arrayed CNTs through the ARB process.The X-ray diffraction pattern of the developed composites showed no peaks for carbon and aluminum carbide.In addition, tensile tests showed that the longitudinal strength of the specimens processed with aligned CNTs was significantly greater than that of the specimens with common randomly dispersed particles.The proposed technique is beneficial for the fabrication of Al–CNT composites with directional mechanical strength.

经形变热处理铜基形状记忆合金的晶粒生长、形状记忆和腐蚀行为(英文)

比较研究了Cu-11.8%Al-3.7%Ni-1%Mn和Cu-11%Al-5.6%Mn形状记忆合金(SMAS)的形状记忆、腐蚀性能。采用光学显微镜(OM)、扫描电子显微镜(SEM)、差示扫描量热法(DSC)、动电位极化、弯曲和拉伸试验,研究了晶粒细化对这些性能的影响。在800°C退火时,在首先的15 s内静态再结晶和动态晶粒长达显示出一个快速的再结晶过程,随后才是晶粒生长。退火15 s后得到的Cu-Al-Ni-Mn和Cu-Al-Mn合金的最小晶粒尺寸分别为90μm和260μm。拉伸试验表明2种合金呈现典型的三阶段曲线,由此可以看出,晶粒细化后合金具有高的断裂应力和应变。显微组织表明,Cu-Al-Ni-Mn合金中存在锯齿状的1??马氏体形态,通过差示扫描量热法也证实了1??和1??共存于Cu-Al-Mn合金中。评估了形变热处理前、后及800°C退火15 min,随后进行水淬的合金的形状记忆性能。另外,采用动电位极化法分析了晶粒细化后合金的腐蚀行为。结果表明,铜溶解过程中主要为阳极反应,Cu-Al-Ni-Mn合金比Cu-Al-Mn合金具有更好的耐腐蚀性。

Semi-hot Stamping as an Improved Process of Hot Stamping

Reducing the forming load, deletion of springback, increasing the formability of sheets as well as producing high strength parts are the main reasons to apply hot stamping process. Hot stamping process and 22MnB5 steels are the state of the art process and grades, respectively; however novel processes and steel grades are under considerations. In the current research, behavior of the steel grade MSW1200 blanks under semi and fully hot stamping processes was characterized. During semi-hot stamping process, the blank was firstly heated to a temperature of about 650℃ and then formed and quenched in the die assembly, simultaneously. Microstructure and mechanical properties of semi and fully hot stamped blanks were studied and the results were compared with those of normally water/air quenched blanks. The hot stamped blanks attained the strength values as high as water quenched blanks. The highest ductility and consequently, the best formability were achieved for the blank which had been semi-hot stamped. It was concluded that for the mentioned steel, semi-hot stamping process could be considered as an improved thermo-mechanical process which not only guaranteed a high formability, but also led to ultra high strength values.

Mechanical and microstructural variations in ECAP of Ti-6Al-4V alloy with equiaxed microstructure

The aim of this study is to investigate mechanical and microstructural variations of Ti-6 Al-4 V acquired through various equal channel angular pressing(ECAP)cycles.The ECAP of Ti-6 Al-4 V alloy with the first equiaxed micros tructure was carried out by an isothermal warm and isothermal die method.EC A pressing carried out on cylindrical samples at 650℃.Mechanical and microstructural investigations were performed concerning Ti-6 Al-4 V in the first state after 2,4,and 8 passes.Optical microscopy(OM)investigation shows that alpha grain size increases and beta grain size decreases with the pass numbers increasing.Beta phase content initially decreases in the first two ECAP passes.The results show that more equiaxed alpha grains are achieved after four ECAP passes.Results of X-ray diffraction(XRD)analysis show that crystallite size decreases with the number of passes increasing.After two ECAP passes,a vivid increase in mechanical strength is observed;however,the increment dramatically slows down by the increasing number of passes.