高硅铝合金标准样品的热变形行为

对高硅铝合金光谱标准样品在应变速率为0.01～1s-1、变形温度为350～500℃条件下的热压缩变形行为进行实验研究。结果表明:高硅铝合金热压缩变形中发生了明显的动态回复与动态再结晶,流变应力随应变速率的增加而增加,随温度的增加而降低;通过线性回归分析计算出高硅铝合金材料的应变硬化指数n以及变形激活能Q,获得了高硅铝合金高温条件下的流变应力本构方程;研究工艺参数(变形温度t、应变速率ε)对晶粒尺寸的影响,确定最佳工艺参数:t=400℃,ε=0.1s-1。     

易切削Cu-Se-Bi合金的高温塑性变形行为

采用Gleeble-1500热模拟机研究了Cu-Se-Bi合金在变形温度为550～700 ℃,应变速率为0.01 ～10.00 s-1条件下的流变应力变化规律和微观组织,并根据试验数据确定了本构方程.结果表明,Cu-Se-Bi合金高温动态再结晶明显降低合金的流变应力,变形量在15%～80%时,流变应力趋于稳定;当应变速率为2.50、10.00 s-1时,流变应力出现波动,温度为700 ℃、应变速率为10.00 s-1、应变在0.09～0.15时应力波动值可达12 MPa;变形量越大,动态再结晶越明显;应变速率越小,晶粒越细小;当温度为600 ℃、变形量为60%、应变速率为0.01 s-1时,平均晶粒尺寸为8.5 μm.     

2519铝合金热变形流变行为

采用Gleeble-1500热模拟机进行高温等温压缩实验,研究了2519铝合金在变形温度为300～450℃、应变速率为0.01～10 s-1条件下的流变变形行为.结果表明:应变速率和变形温度对合金流变应力的大小有显著影响,流变应力随温度升高而降低,随应变速率的提高而增大,在应变速率ε＜10 s-1条件下,流变应力开始随应变增加而增大,达到峰值后趋于平稳,表现出动态回复的特征;而在ε=10 s-1,t≥350℃的变形条件下,合金发生了局部动态再结晶.可用包含Arrhenius项的Zener-Hollomon参数描述2519铝合金高温塑性变形时的流变行为.     

铸态42CrMo钢的高温塑性变形特性

利用Gleeble 1500D热模拟试验机,在应变速率为0.01~10 s-1、变形温度为1000~1150℃、变形量为60%的条件下对铸态42Cr Mo钢的高温塑性变形特性进行了研究。结果表明,材料的流变应力随变形温度的升高而减小,随应变速率的增大而增大;试验钢的峰值应力激活能Q=325.63 k J/mol,稳态应力激活能Q=271.84 k J/mol;变形过程中动态再结晶晶粒平均尺寸随温度的增大而增大,随应变速率的增大而减小,其自然对数与Zener-Hollomon参数的自然对数成线性关系。     

变形程度对铸态AZ31镁合金动态再结晶的影响

研究了铸态AZ31镁合金在温度为250～425℃、变形量为10%～40%、应变速率为0.01 s-1的条件下的热压缩时动态再结晶的变化规律,分析了流变应力与变形程度的关系。结果表明:铸态AZ31镁合金在应变速率为0.01 s-1的条件下进行热压缩变形,变形程度达到40%时,材料会发生断裂;当应变速率和变形温度一定时,流变应力随变形程度的增大不断增加,在达到峰值后逐渐降低,表现出明显的动态再结晶的特征;且随变形程度的增大,动态再结晶晶粒越来越多。     

AM80-xSr-yCa镁合金高温压缩变形行为

采用Gleeble-1500热模拟实验机对一种新型AM80-xSr-yCa镁合金进行高温压缩变形实验,研究其在温度300℃~450℃、应变速率0.01s-1~10s-1条件下的流变行为。高应变速率下,试样的变形热带来的温升不可忽略,对真应力-真应变的测量值进行相应修正后,求得了本构方程中的系列常量。结果表明,应变速率和变形温度的变化,强烈影响着合金流变应力的大小,流变应力值随变形温度的降低和应变速率的提高而增大;金相组织观察表明,动态再结晶是该实验条件下晶粒细化和材料软化的主要机制,再结晶的程度主要受变形参数影响。变形温度越高,变形量越大,动态再结晶进行的越充分;应变速率越大,再结晶平均晶粒尺寸就越小。     

Mg-13Gd-4Y-2Zn-0.5Zr合金热压缩行为及晶粒尺寸的研究

采用Gleeble-3500热压缩实验机对Mg-13Gd-4Y-2Zn-0.5Zr合金在温度360～480℃、应变速率0.001～1 s-1、最大变形程度为60%的条件下进行高温压缩实验研究。分析了应变速率和变形温度对该合金在高温变形时流变应力的影响,引入温度补偿应变速率因子Z构建合金高温流变应力的本构方程;研究了合金在不同压缩条件下的组织变化及动态再结晶晶粒尺寸,为后续有限元组织模拟提供了实验依据。结果表明:该合金的真应力-真应变曲线具有动态再结晶曲线的特征。动态再结晶的再结晶晶粒尺寸随温度的降低、应变速率的增大而减小;而且峰值应力也随再结晶晶粒尺寸的减小而增大。     

7136铝合金的热变形与动态再结晶行为

明确7136铝合金的热变形和动态再结晶行为对于制定合理的加工工艺参数具有重要意义。试验亦分析了7136铝合金试样在变形温度为350℃～470℃、应变速率为0. 01 s-1～10 s-1条件下的热变形与动态再结晶行为,建立了合金的流变应力模型,并通过挤压试验和数值模拟验证了流变应力本构方程的合理性。结果表明,7136铝合金在350℃条件下进行热加工发生动态再结晶,再结晶百分数随温度升高而增加,随应变速率增加而减少:应变速率为0. 01 s-1、变形温度由375℃上升到450℃时,再结晶百分数由6. 8%逐渐增加至8. 2%;变形温度为400℃、应变速率由0. 01 s-1提高至10 s-1时,再结晶百分数由7. 6%逐渐减少至4. 9%。所获得的本构方程用于挤压过程的数值模拟,稳态阶段模拟与实际载荷位移曲线误差不超过5%。7136铝合金热挤压过程应选择较低的挤压温度和较高的挤压速度,以降低其动态再结晶百分数。     

锻态TB6钛合金热变形行为及组织演变

在THERMECMASTER-Z型热模拟试验机上,对锻态TB6钛合金在真应变为0.92、变形温度为800℃～1150℃、应变速率为0.001s-1～1s-1的条件下进行等温恒应变速率压缩试验,分析合金在β单相区条件下的热变形特点,并观察金相组织。结果表明,应变速率对合金流动应力的影响较显著;而变形温度对合金流动应力的影响在较高应变速率时较大,在较低应变速率时较小。动态再结晶晶粒尺寸和动态再结晶体积分数,随温度的升高而增大,随应变速率的增大而减小。从晶粒细化和动态再结晶组织均匀性考虑,当真应变为0.92时,变形温度选择在950℃～1050℃之间,应变速率选择在0.01s-1为宜。     

建筑Al-Mn-Er-Zr合金屋面板的热变形行为研究

在Gleeble 3500热模拟试验机上,对半连续铸造Al-Mn-Er-Zr合金棒坯进行变形温度350～500℃、应变速率0. 01～10 s-1的高温压缩试验,建立了高温热变形稳态流变方程,并对流变曲线进行了温升修正。结果表明,在相同应变速率下,变形温度的升高会使Al-Mn-Er-Zr合金更容易发生动态再结晶;在相同变形温度下,随着应变速率的增大,Al-Mn-Er-Zr合金中流线组织逐渐粗化,锯齿化程度增大,动态再结晶晶粒有所细化。进行了Al-Mn-Er-Zr合金的应力-应变本构方程建立与求解,得出了在变形温度350～500℃、应变速率0. 01～10 s-1时的高温变形稳态流变方程;高温压缩过程中由温升造成的计算应力与实测应力的误差在10%以内,高温热变形稳态流变方程能够较好的表征Al-Mn-Er-Zr合金的高温流变行为。     

RHEOLOGY FEATURE OF SIMPLE METAL MELT

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

Secondary Recrystallization Behaviors of Grain-Oriented 6.5 wt% Silicon Steel Sheets Produced by Rolling and Nitriding Processes

By rolling and nitriding processes, 0.23- to 0.3-mm-thick grain-oriented 6.5 wt% silicon steel sheets were produced. The core losses of grain-oriented 6.5 wt% silicon steel at frequencies ranging from 400 Hz to 20 k Hz were lower than that of the grain-oriented 3 wt% silicon steel with the same thickness by 16.6–35.8%. The secondary recrystallization behavior was investigated by scanning electron microscopy, energy-dispersive spectroscopy, and electron backscattered diffraction. The results show that the secondary recrystallization in high-silicon steel sheets develops more completely as the nitrogen content increases after nitriding, secondary recrystallized grain sizes become larger, and the sharpness of Goss texture increases. Because more {110}116 grains in the subsurface and the central layer of the sheets have a lot of 20°–45° high-energy boundaries in addition to Goss grains, {110}116 can be the main component through selective growth during secondary recrystallization when the inhibitor quantity is not enough and inhibitor intensity is weaker. The increases in nitrogen content can increase the inhibitor intensity and hinder abnormal growth of a mount of {110}116 grains and therefore enhance the sharpness of Goss texture.     

LASER CLADDED TiCN COATINGS ON THE SURFACE OF TITANIUM

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

Microstructure,Mechanical Properties and Corrosion Behavior of Extruded Mg–Zn–Ag Alloys with Single-Phase Structure

Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag(wt%,x=0.2,0.5 and0.8)alloys with single-phase crystal structure were prepared by backward extrusion at 340°C.The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure,but the elongation firstly increases from12%to 19.8%and then decreases from 19.8%to 9.9%with the increment of Ag concentration.The tensile yield strength,ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142,234 MPa and 19.8%,respectively,which are the best mechanical performance of Mg–Zn–Ag alloys in the present work.The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test,which could be explained by the single-phase and uniformly distributed grain structure,and the fewer twinning.     

STUDY ON PROPERTIES OF PULSE ELECTRODEPOSITED RE-Ni-W-P-SiC COMPOSITE COATINGS

The effects of pulse frequency f and duty cycle r on the deposition rate, composition, morphology, and hardness of pulse electrodeposited RE （rare earth）-Ni-W-P-SiC composite coatings have been studied. The results indicate that pulse current can improve the deposition rate of RE-Ni-W-P-SiC composite coatings; W, P, and SiC contents in the coating decrease with the increase of pulse frequency and reach the lowest value at f = 33Hz, whereas the RE content in the composite coatings increases with the increase of pulse frequency. SiC content decreases with the increase of duty cycle, W content reaches the lowest value, and P content reaches the highest value at r = 0.4; pulse current and RE can lead to smaller size of the crystalline grains; however, the effects of different pulse frequency and duty cycle on the morphologies of RE-Ni-W-P-SiC composite coatings are not obvious. The hardness of RE-Ni-W-P-SiC composite coatings is the highest when the duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz. At the same pulse frequency, the hardness of RE-Ni-W-P-SiC composite coatings at r= 0.8 is higher than that at r= 0.6.