The Mg−Al composite rods of aluminum core-reinforced magnesium alloy were prepared by the extrusion−shear(ES)process,and the microstructure,deformation mechanism,and mechanical properties of the Mg−Al composite rods were investigated at different extrusion temperatures and shear stresses.The experimental results show that the proportion of dynamic recrystallization(DRX)and texture for Al and Mg alloys are controlled by the combination of temperature and shear stress.The texture type of the Al alloys exhibits slight variations at different temperatures.With the increase of temperature,the DRX behavior of Mg alloy shifts from discontinuous DRX(DDRX),continuous DRX(CDRX),and twin-induced DRX(TDRX)dominant to CDRX,the dislocation density in Mg alloy grains decreases significantly,and the average value of Schmid factor(SF)of the basalslip system increases.In particular,partial grains exhibit a distinct dominant slip system at 390℃.The hardness and thickness of the bonding layer,as well as the yield strength and elongation of the Mg alloy,reach their maximum at 360℃as a result of the intricate influence of the combined temperature and shear stress.
Jian-xing ZHAOChao-wei ZENGTing YUANWei PENGZhen-wei SUNOu ZHANGHong-jun HU
氨分解作为一种很有前景的现场制氢技术,关键在于开发出廉价、高性能的催化剂。本研究通过共沉淀法合成系列Ni_(x)Mg_(75–x)Al_(25)类水滑石化合物(HTlc)作为前驱体,经过焙烧和还原处理制备负载型高分散Ni/Mg(Al)O催化剂并用于氨分解制氢,采用不同研究手段对样品进行了表征,考察了Ni含量和氨还原对催化性能的影响。结果显示,HTlc前驱体经过焙烧分解形成Mg(Ni,Al)O固溶体,Ni物种与载体之间存在较强的相互作用,经750℃氨还原得到高分散Ni金属纳米颗粒,其平均晶粒尺寸为5.9~7.7 nm。质谱分析表明,氨还原过程中无氮氧化物(NOx)生成,同时750℃氨还原与氢还原催化剂的活性相当,说明氨是一种合适的还原气。催化剂活性随着Ni含量和还原温度升高而增加。其中,750℃氨还原Ni_(20)Mg_(55)Al_(25)催化剂在30000 m L·g^(–1)cat·h^(–1)、600℃下的氨转化率为98%,且在100 h反应过程中转化率保持不变,Ni金属无明显烧结现象,催化剂表现出良好的活性、稳定性和抗烧结性能。
