Materials Science Forum Vols. 610-613

Abstract: In this paper，the influence of adding Al on the discharge capacity and cycle stability of amorphous MgNi-based hydrogen storage alloys were investigated. Amorphous Mg1-xAlxNi (x=0, 0.1, 0.2, 0.3) alloy powder was prepared successfully by mechanical alloying (MA). X-ray diffraction (XRD) results show that after ball milling with 15h, MgNi alloy formed completely amorphous phase. But for Mg1-xAlxNi (x=0.1, 0.2, 0.3) alloy, it took 30h. It can be concluded that Al partial substituting Mg would decrease the amorphous phase forming ability of Mg-Ni Based Alloy. The discharge capacities and cycle stabilities of these alloys were tested. Compared with amorphous MgNi alloy, the discharge capacities of Mg1-xAlxNi (x=0.1, 0.2, 0.3) alloy were decreased slightly, but the cycle stabilities were significantly enhanced. Mg0.9Al0.1Ni alloy showed the largest discharge capacity and Mg0.8Al0.2Ni alloy showed the best cycle stability. Over all, ternary Mg0.8Al0.1Ni alloy showed the best synthesis properties.

Abstract: The elasto-plastic behavior and the drawing limit of a kind of magnesium alloy tube were investigated based on the foundational theories of the larger deformation of material and continuum damage constitutive model. The corresponding finite element numerical algorithm was developed based on the constitutive model. The non-mandrel drawing limit graph according to the diameter at different tube thickness of an AZ31B tube with diameter 10mm at 250°C and drawing velocity 100mm/s was achieved, and safe & unsafe area got partitioned. The maximum damage value was evaluated to be 0.324 according to height reduction ratio limit and rigid-plastic FE analysis.

Abstract: Hydrogen storage in solid hydrides is the most attractive method of on-board hydrogen storage in fuel cell for cars. Mg metal exhibits a high-storage capacity by weight and has been considered a group of potentially attractive candidates for solid-state hydrogen storage. In this study, mechanochemical synthesis of nanocrystalline Mg-based hydrogen storage composites from various starting materials in specialized hydrogen ball mills has been achieved. The reactive synthesis process and the hydrogen desorption behaviors of the composite hydrides were investigated by X-ray diffraction (XRD), thermogravimetric and differential scanning calorimetry (TG-DSC). The results show that nano-sized MgH2 and Mg(AlH4)2 could be directly synthesized by pure Mg and pretreated Al powder, as well as Mg-Li-Al alloy powder. Alloying element Li could remarkably promote the synthesis of magnesium alanate, the product composite hydrides releasing 6.2wt% H2 through multi-step decompositions, of which the starting endothermic peaks are as low as 65°C.

Abstract: The Mg-based hydrogen storage alloys of Mg2Ni (A2B), Mg1.7Al0.3Ni, Mg2Ni0.8Cr0.2 and Mg1.8Al0.2Ni0.8Cr0.2 were successfully prepared by mechanical alloying and sintering. The effect of the substitution side A by Al and side B by Cr on microstructure of Mg2Ni alloy has been studied by XRD and SEM. The results indicated that the synergistic effect occurred when the elements Al and Cr coexist in Mg2Ni alloy, element Cr could inhibit the formation of non-hydrogen-adsorption phase of Al3Ni2, in addition, it will promote the formation of hydrogen-adsorption phase of Mg3AlNi2; the existence of Al could inhibit the formation of non-hydrogen-adsorption phase of -[ Cr, Ni].

Abstract: The corrosion properties of Mg-Al-Sr alloy was characterized with comparison to AZ91D alloy. With the addition of Mg-Sr master alloy, the grain size of Mg alloy refined and the corrosion resistance was improved. The experimental results indicated that the formation of small amount of Al4Sr phase was favorable to improve the corrosion resistance. However, with the increase of Al4Sr stripy phase, the area ratio of cathode to anode will increase, resulting in the decrease of corrosion resistance potential.

Abstract: In this paper, the influence of the types and addition dose of MgO expanding agent and the age of cement on expansion value and expansion performance of cement based material added with MgO expanding agent was systematically studied.The expansion characteristics of cement based material added with MgO expanding agent or calcium sulphoaluminate expanding agent were compared. The expansion of such material increases with the addition dose of MgO expanding agent and cement mortar age. During the test period, the expansion of cement based material increases continuously. The light-burned MgO expanding agent modified by CaO expanding agent is able to increase the 28d expansion of such material effectively. The temperature of calcination for the heavy-burned MgO expanding agent is higher than that of light-burned one, thus the heavy-burned MgO expanding agent has a rather dense structure with slow hydration rate and gives a small expansion of the cement based material at early age, showing an obvious expansion delay. The calcium sulphoaluminate expanding agent gives most expansion of the material in the early 28d and there is small expansion at middle and later age of the material.

Abstract: A new maching method of pretreatment magnesium alloy surface was design based on abrasive belt grinding technology, which offered a kind of technology for magnesium alloy tube surface machining. Experimental results indicated that abrasive grain granularity, belt speed and workpiece feed speed play an important role in grinding for magnesium alloy tube surface, which made magnesium alloy tube surface roughness from 0.22 um to 2.93 um with 400 grade to 80 grade on abrasive grain granularity of belt, raise the belt speed to reduce surface roughness, but raise workpiece feed speed to deteriorate roughness.

Abstract: Mg-Sr alloy was prepared by the vacuum synchronous reduction method at a temperature of 1100°C. The phase composition of the reaction product and slag was analyzed by XRD. Results showed that Mg17Sr2 and α-Mg were formed in the product while Ca2SiO4 and Sr2SiO4 existed in the slag. DSC-TG curves obtained from thermal analysis of the reduction process indicated that vacuum was an essential condition in the preparation of Mg-Sr alloy by synchronous thermal reduction method when temperature was below 1200°C.

Abstract: In this study, plasma treatment using Ar and H2 and plasma polymerization with trimethylsilane (TMS), were carried out to create the interface film systems with a structure of Mg/plasma interlayer/cathodic electrophoretic coating (E-coat) for a magnesium (Mg) alloy AZ31B. The interface adhesion of the coating system was evaluated using N-methylpyrrolidinone (NMP) paint removal test and ASTM tape test conducted under dry and wet conditions. Plasma TMS film could stick the Mg substrate more strongly than E-coat.The surface of samples with different interlayer treatment after NMP test has been observed by SEM. The potentiodynamic study performed on the E-coated samples showed a noticeable reduction of corrosion current, three orders of magnitude less than bare Mg. Salt spray test also was done to confirm the resistance corrosion of E-coat. It was found that plasma interface treatment has the ability of increasing the adhesion of E-coat on Mg alloy more or less, thus restrict access to damaging species that exist in Cl- aqueous environments.

Abstract: Magnesium alloys are among the best light-weight structural material with a relatively high strength-to-weight ratio end excellent technological properties. Therefore, magnesium attracts special attention of researchers working in automotive and aircraft industry. This work paid the efforts to the structural components made out of magnesium alloy AM60 such as chassis, transmission case in automotive, where the components are subject to cyclic loading after being pre-loaded. In this study, the cyclic stress-strain behaviors were investigated by strain-controlled fatigue testing. In order to investigate the effects of R-ratio on mean stress relaxation, the R-ratio ranged from 0.1 to 0.7 at the strain amplitude of 0.3%. The experimental results indicate that the mean stress relaxation increases with the increasing R-ratio. A constitutive model was proposed to simulate the mean stress relaxation. The calculation results show that the constitutive model developed in this work is capable of reproducing the stress relaxation behaviors of magnesium alloy AM60 under strain control.