AZ31镁合金热轧开坯变形行为的有限元模拟

采用二维弹塑性大变形热力耦合有限元法(FEM),对半连续铸造AZ31镁合金热轧开坯过程第一道次进行模拟,分析变形区内轧件的应力场、应变场的分布及整个热轧过程中的温度场的变化规律.实验结果表明:在轧件变形区内,等效应力沿轧制方向逐渐增大,在中性面附近达到最大值54.1 MPa,随后又逐渐减小;靠近轧件表层σ_x为压应力,靠近心部为拉应力,在变形区σ_y主要为压应力,由表面到中心σ_y逐渐减小;等效应变沿轧制方向逐渐增大,在轧件出口处达到最大值0.253;在整个轧制过程中,轧件内部节点的温度变化缓慢,而表面节点的温度变化剧烈,轧制完成后,表面温度从500℃降低到467℃,中部温度从500℃升高到503.1℃,心部温度从500℃升高到502.2℃.     

双辊铸轧镁合金薄带冷轧实验研究

采用AZ31镁合金铸锭在实验室立式等径双辊铸轧机上进行铸轧试验;对铸轧带坯直接进行冷轧和冷轧后退火处理.研究了AZ31镁合金薄带立式双辊铸轧工艺及铸轧带坯进行冷轧、轧后退火过程的组织演变行为.采用合理的工艺参数,成功铸轧出镁合金薄带,同时由于双辊铸轧快速冷却和压力下凝固成形技术特点,改善了镁合金的凝固组织.对铸轧镁合金带坯直接进行冷轧,最大变形量可以达到40.7%.经过冷轧后的镁合金板材,在350℃下退火30~60 min,可以获得平均晶粒直径为9~10μm的等轴晶细晶组织.     

钙在镁合金熔炼中的阻燃机理

熔炼了钙的质量分数为0.5%~5.0%,铝的质量分数为9.0%的10种镁合金,研究了Ca的加入对合金阻燃效果的影响.分别取定量的10种合金在700℃的高温下进行氧化增重的测量,并对合金表面的氧化形貌进行了观察.实验结果表明:镁合金加入钙后,其表面在高温下生成了CaO及少量MgO的复合致密氧化膜,这层氧化膜隔绝了空气,阻止了镁的燃烧;当钙的质量分数为3.5%时,可起到良好的阻燃效果.     

Sr对Mg-5Al-0．8Ca-0．2La镁合金显微组织及高温性能的影响

研究了Sr对Mg-5Al-0.8Ca-0.2La镁合金显微组织与室温和高温力学性能的影响.实验结果表明,Sr的加入显著细化了基体合金的显微组织,抑制了β-Mg17Al12相的析出;并且在晶界上析出了Mg-Al-Sr,Al2Ca和Al11La3耐热相,提高了晶界的高温稳定性.Sr的加入虽然导致合金的室温抗拉强度和延伸率下降,但提高了合金高温抗拉强度,也略提高了室温和高温屈服强度.     

有效时间概率关联规则在商品推荐系统中的应用

在关联规则挖掘中,大量的数据是多维的,且带时间性,根据实际的应用,对传统的算法进行了改进,提出了在商品推荐系统中构建的模型,并与类似算法进行了比较.采用了本文提出的算法后,能够挖掘出小概率项目中蕴涵的关联规则,并考虑到时间的因素,去除了多余的杂质数据,而Apriori算法则无法做到这点.     

表面活性剂从碱性氰化液中萃取金机理研究第三相的产生

利用Fourier变换红外光谱(FTIR)、核磁共振(³¹P-NMR)、激光光散射(DLS)等方法研究了萃取后负载金有机相的溶液结构。实验结果表明,随着有机相金浓度和表面活性剂浓度逐渐增加,有机相含水量增加,有机相中磷酸三丁酯(TBP)的磷氧基伸缩振动向低频移动,核磁共振(³¹P-NMR)的化学位移向高场移动;同时有机相中开始有直径16nm左右的聚集体形成;随着胶团逐渐长大,有机相分成两相即产生第三相;第三相中有直径4nm左右的胶团存在。     

Microstructural formation of semi-solid AZ91D alloy stirred by electromagnetic field

With the help of an electromagnetic stirring device, alloy melt quenching and EBSD (electron back scatter diffraction)analysis technology, the microstructure of the semi-solid AZ91D magnesium alloy slurry stirred by rotational electromagnetic field under different stirring power conditions has been studied. The results show that the size of primary α-Mg phase is reduced obviously when the solidifying alloy melt is stirred by rotational electromagnetic field, moreover, the primary α-Mg grains are changed to fine rosette grains or spherical grains which are proved to belong to the different grains in three-dimension by the EBSD analysis technology. The results also show that the stirring power is an important processing parameter in the preparation of the semi-solid AZ91D magnesium alloy slurry. The larger the stirring power, the finer the primary α-Mg grains, the less the rosette primary α-Mg grains, and the more the spherical primary α-Mg grains. Theoretical analysis indicates that a stronger flow motion leads to a more even temperature field and solute field and a stronger man-made temperature fluctuation in the alloy melt so that the specially fine rosette and/or spherical primary α-Mg grains are formed in the semi-solid AZ91D magnesium alloy slurry.     

Effect of RE on the ignition-proof,microstructure and properties of AZ91D magnesium alloy

The magnesium alloy is prone to burn during die-casting, which limits its applications severely, so the effect of adding rare earth (RE) on the ignition-proof of AZ91D Mg alloy is studied. The results indicate that the addition of mischmetal RE elements has a remarkable influence on the ignition-proof property of the magnesium alloy. It is found that the ignition temperature of the magnesium alloy can be greatly raised by adding a proper amount of RE. When the amount is 0.1 wt%, the ignition temperature reaches 877°C which is 206°C higher than that of AZ91D without RE and the mechanical properties of the alloy are also improved. However, the amount of RE must be properly controlled because too much RE would induce grain coarsening and reduce the mechanical properties.     

中国省域投资环境的对比评价与分析

采用层次分析（AHP）与主成份分析相结合的方法,对中国大陆31个省市区的投资环境进行了总体性评价;以第三产业为例,采取关键要素评价法结合主成份分析,对省省（市区）域的产业对象性投资环境进行了评价,并就各评价结果作了简要对比分析。