Mechanical behavior of Al-Zn-Mg-Cu alloy under tension in semi-solid state

In order to study the hot fractures in relation to the semi-solid processing, the tensile tests of an extruded 7075 aluminum alloy which is based on Al?Zn?Mg?Cu system were carried out in the high temperature solid and semi-solid states at different strain rates. The results show that the tensile behavior can be divided into three regimes with increasing the liquid fraction. The alloy first behaves in a ductile character, and as the temperature increases, the fracture mechanism changes from ductile to brittle which is determined by both of liquid and solid, and lastly the fracture mechanism is brittle which is totally dominated by liquid. At strain rates of 1×10?4, 1×10?3 and 1×10?2 s?1, the brittle temperature ranges are 515?526, 519?550 and 540?580 °C, respectively. Two equations which are critical for tensile behavior are proposed.

Thermal deformation behavior and mechanism of intermetallic alloy Ti2AlNb

The deformation behavior and mechanism of Ti2AlNb-based alloy were experimentally investigated at elevated temperatures. Firstly, the stress?strain relationships at different temperatures and strain rates were investigated via uniaxial tensile testing. Then, formability data, as determined by examining the deep drawing and bending abilities, were obtained through limiting draw ratio (LDR) and bending tests. Finally, metallographic experiments and fracture morphology investigations were conducted to examine the thermal deformation mechanism of the alloy. The results showed that as the temperature increased, the total elongation increased from 13.58% to 97.82% and the yield strength decreased from 788 to 80 MPa over the temperature range from 750 to 950 °C at a strain rate 0.001 s?1. When the temperature reached 950 °C, the strain rate was found to have a great influence on the deformation properties. The plastic formability of the sheet metal was significantly improved and a microstructuraltransformation of O toB2 andα2 occurred in this temperature region, revealing the deformation mechanism of its plasticity.

Wrinkling behavior of magnesium alloy tube in warm hydroforming

In tube hydroforming with axial feeding,under the effect of coupled internal pressure and axial stress,wrinkles often occur and affect the forming results.Wrinkling behavior of an AZ31B magnesium alloy tube was experimentally investigated with different loading paths at different temperatures.Features of wrinkles,including shape,radius and width,were acquired from the experiments,as well as the thickness distribution.Numerical simulations were carried out to reveal the stress state during warm hydroforming,and then the strain history of material at the top and bottom of the wrinkles were analyzed according to the stress tracks and yielding ellipse.Finally,effects of loading paths on expansion ratio limit of warm hydroforming were analyzed.It is verified that at a certain temperature,expansion ratio limit can be increased obviously by applying a proper loading path and realizing enough axial feeding.

Research progress of aluminum alloy automotive sheet and application technology

Pretrcatment technology is deeply discussed to explain its importance in guaranteeing properties and form- ability of aluminum alloy automotive sheet. Some typical applications of aluminum alloy automotive sheet to automotive industry are listed. Based on the author＇s knowledge and recognition and research progress presently, the important re- search contents about aluminum alloy automotive sheet are emphasized. Reducing cost and price of sheet and going deeply into application research are the main work for expending the application of aluminum alloy automotive sheet in the automobile.

Prediction on hot deformation behavior of spray-formed 7055 aluminum alloy via phenomenological models

Hot compression tests in the temperature range of 340-450 ℃ and strain rate range of 0.001-1 s^-1 of spray-formed 7055 aluminum alloy were carried out to study its hot deformation behavior. Three phenomenological models including Johnson-Cook, modified Fields-Backofen and Arrhenius-type were introduced to predict the flow stresses during the compression process. And then, a comparative predictability of the phenomenological models was estimated in terms of the relative errors, correlation coefficient（R）, and average absolute relative error（AARE）. The results indicate that Johnson-Cook model and modified Fields-Backofen model cannot well predict the hot deformation behavior due to the large deviation in the process of line regression fitting. Arrhenius-type model obtains the best fit through combining the effect of strain rate and temperature.

Synthesis and compressive fracture behavior of a CuZr-based bulk amorphous alloy with Ti addition

Cu46Zr46A14.8Ti3.2 bulk metallic glass （BMG） was successfully synthesized by copper-mold casting and the mechanical properties at room temperature were measured by compression tests. The structure and thermal characteristics were analyzed by XRD and DSC, and the fracture surface morphology was examined by SEM. The glassy alloy with 4 mm in diameter shows an high fracture strength of 1 960 MPa, with an improvement of about 20% compared to the ultimate compression fracture strength of the Cu46Zr46A18 BMG, which suggests that the Ti addition improves the compression fracture strength. The different degrees of the adiabatic heating induce four types of fracture features： a vein-like structure, an elongated and striated vein pattern, melting and smooth regions. The elongated and striated vein patterns as well as the melting region show that enormous strain energy is released, which causes significant adiabatic heating. Furthernaore, many micro-cracks observed in the smooth region are caused by the strong shear force. In addition, the strong shear force leads to many shear bands as well as the melting in the lateral surface.

Evaluation of pitting corrosion of thixoformed A356 alloy using a simulation model

Pitting behavior of thixoformed A356 alloy, with different reheating temperatures, was evaluated. Linear sweep voltammetric tests were used to study the pitting behavior of thixoformed, rheocast and gravity-cast A356 alloy in a 3.5% NaCl solution. A simulation method was also used in order to identify local galvanic corrosion current density between local galvanic couples. The results obtained show that the resistance to pitting corrosion of the thixoformed samples formed at 600 ℃ is higher than that of the samples formed at 610 ℃ as well as rheocast and gravity-cast samples. These results could be explained by morphological aspects of silicon phase as well as the area effect as related to galvanic corrosion between silicon particles and eutectic aluminum phase.

Determination of Optimal Cash Position of Mutual Fund

Cash position, held by mutual fund with purpose to satisfy investors′ redemption, will inevitably generate certain amount of cost. In this paper, the total cost caused by cash position is divided into opportunity cost and shortage cost, and a model is constructed to describe the relationship between total cost and cash position along with investors′ purchase and redemption, from which the formula of optimal cash position is deduced. Finally, the adjustment of optimal cash position in different market situations is discussed.

Plastic forming behavior of axisymmetric bimetal products with rotary swaging

In this paper,an elasto-viscoplastic three-dimension(3D) finite element model is developed to simulate the processing of bimetal tube with rotary swaging. Through simulation,the effects of high-frequency pulse stroking on the distribution and histories of stress,stain and loading are clarified. The stress in inner tube is compressive and higher than the minimum bonding force. Meanwhile,the stiffness of inner tube impacts outer tube extension in length.

Analysis of the Economical, Ecological and Quality Advantages Consequent Resulting from Initiation of Technology Integrated in Metallurgy

Metallurgical sector plays an important role in the economy of each country because steel products present essential raw material for basic industries. Changes in the sectors of iron, steel and non-ferrous metals and the current development of technology forces the steel mills increased productivity, reduce production costs while ensuring to obtain a product with the required properties and to improve the competitiveness of enterprises in the global market. Currently, the most popular in meeting these requirements, enjoys a method of integration which combines individual operations into one integrated whole. The use of modem, perfectly designed, fully automated design of mechanical, hydraulic and measurement allowed us to achieve an innovative line of production. This article presents the general characteristics of the steel industry and a description of the latest integrated technology currently used in foundries and rolling mills. It also presents examples of the use of integrated technologies in metallurgy and the effects of economic, environmental and quality resulting from their use on an industrial scale.

he U.S. Mortgage Crisis

The financial crisis of 2008 left the U.S. economy in a state of severe recession, which is still being felt all over. This has also left the government in a frantic condition to rebuild the financial markets from the bottom up. What started out with excessive bank lending on mortgages lead to the mortgage crisis and a ripple effect on the economy. The cancer has spread globally, affecting every major marketplace and all the major states in the U.S.. Our economy is still very fragile because of this crisis, but eventually we will recover in a few years time to achieve robust economic growth. Long standing cultural pressures in the United States maintained that home ownership was necessary to be a part of the American Dream, and this cultural stance was reinforced by Clinton in 1994, when he enacted a program to raise home ownership to more than two-thirds of all adults. With the tacit blessing of the Federal Government, many mortgage companies sprung up, that catered to those in lower income brackets, offering them the mortgages that many did not have the financial sophistication to understand and deliver. Coupled with the skyrocketing costs of property taxes, insurance, and maintenance costs, many homeowners found themselves unable to pay their mortgages. The whole industry tanked, causing displacement of people and increased unemployment. The lenders of these mortgages sold the notes to investment bankers, and they were sold as high-quality investment grade securities. The major rating agencies were complacent in this tactic, causing rapid default rates on these mortgages; many commercial and investment banks got caught in this crisis. The prices of homes continue to decline, and many homeowners find themselves under water on their mortgages. It was found that in 2010, the U.S. government was responsible for nine out of every ten mortgages issued, which caused further problems with Fanny Mae and Freddie Mac. The crisis is still continuing, with no end in sight. The analysis was based on the data analysis and readings from the journal, as well as various Wall Street commentaries.

摆阔不足道

世界变化真快,昨天还是谁穷谁光荣,是依靠对象,今天变成财大气粗,潇洒地挥霍成为时尚。新闻媒介对此又津津乐道,且乐此不倦,无意关注全国未彻底解决温饱的8000万人的吃饭穿衣,拼命追踪某名人的狗每天伙食费200元还是300元。摆阔、崇阔、效阔的浊流越流越急。 阔老阔少们,不管中国还处于初级阶段,俨然以石油大王的派头,早已不满足古人用蜡当柴烧,做“锦步障”50里,狂砸名贵珊瑚式的摆阔,而是你用6万元请我吃顿饭,我拿出35万元回报,决非“一支烟,四两油;一顿饭,一头牛”的水平。

Correlation between supercooled liquid region and crystallization behavior with alloy composition of La-Al-Cu metallic glasses

Bulk metallic glasses (BMGs) with large supercooled liquid region are promising materials for superplastic forming. In this paper, we demonstrate a microstructure-based strategy to pinpoint the composition with the largest supercooled liquid region in La 86 x Al 14 Cu x (x=16 at%-20 at%) metallic glass system. By monitoring the changes in crystallization behavior of the glassy alloys with composition to search for the alloys exhibiting eutectic crystallization, the glassy alloys with the largest supercooled liquid region in the given alloy system can be found. The metallic glasses with Cu contents of 16 at%-19 at% exhibited two crystallization peaks, and the primary crystallization product was identified to be α-La by means of DSC, XRD and TEM. The increase in Cu content resulted in the decay of the primary crystallization peak and the increase in onset temperature of crystallization, leading to the enlargement of supercooled liquid region. By further suppressing the α-La primary crystallization with increasing Cu content up to 20 at%, the eutectic crystallization of α-La and LaCu 13 through one crystallization reaction occurred upon heating, where the largest supercooled liquid region of 65 K for La 66 Al 14 Cu 20 glassy alloy was located. This study indicats that, in a given glassy alloy system, a larger supercooled liquid region can be achieved by optimizing the alloy compositions to suppress the primary crystallization.