Research On Manufacturing Technique Of Wrought Magnesium Alloy Strips And Sheets By Powder Rolling And Related Powder Metallurgy Method

Magnesium alloys being recognized as green materials in the 21st were received increasing attention. In all magnesium alloys cast Mg alloys were widely used by now. While being possessed with higher mechanical properties, wrought magnesium alloys would be one of the attractive directions of magnesium alloys development in the future. Magnesium has a hexagonal close packed (hcp) crystal structure with a limited number of operative slip system at room temperature, and thus cold deformation of magnesium alloys were difficult. Deformation at high temperature was also faced oxidation. So the technology of manufacturing wrought magnesium alloys strips was immature. Powder rolling technology which was conceptual simple, low operating cost and in possession of the advantages of powder metallurgy (PM) was used in many different industries for a wide variety of materials. In this paper, laboratory scale ordinary duo mill was used in manufacturing of magnesium alloys by powder rolling. The powders used in experiments were bought in home country. The particle size were: 10~80 mesh and 200 mesh Mg, 60~80 mesh and 200 mesh Al and 300 mesh Zn, and the mixing mode were: 10~80 mesh Mg and 60~80 mesh Al, remarked by No. Ⅰ, 200 mesh Mg, 200 mesh Al and 300 mesh Zn, remarked by No. Ⅳ. Metallographic analysis, grain size analysis, SEM analysis, X-ray analysis and DSC analysis were employed in the experiments. Powder shape, grain size and its distribution and loose density of powders were analyzed. The microstructures of Mg ingot which produced Mg powders were observed. The influence of roll gap, feeding height and the width of green strips on the thickness and the density of green strips were analyzed. The microhardness of green strips produced in different technology were analyzed. The microstructures and the macro-micro deficiency of green strips were observed. Green strips were sintered at 400~ 600 ℃, and the microstructures of sintered strips observed. The phase transformation in the process of sintering and the phase of sintered strips were analyzed. The results showed that continuous green strips could be manufactured by the laboratory scale ordinary duo mill (roll diameter is 170mm and roll velocity is 0.2 m / s). The properties of powder, roll gap, feeding height and the width of green strips had the influence on the thickness and density of green strips during roll compaction. With the increasing of roll gap the thickness of green strips increased and the density decreased. The best roll gaps for No. Ⅰand No. Ⅳmixing powders were 0.10mm and -0.10mmm, respectively. When the roll gap exceeded 0.25mm and 0.15 mm respectively, roll compaction would not be realized. With the increasing of feeding height the thickness and the density of green strips increased. When the feeding height exceeded 20 mm, the influence of it was insignificant. With the increasing of the width of green strips the thickness of green strips increased and the density of green strips decreased. The suitable width of green strips was 10 cm. The microhardness of No. Ⅳgreen strips was higher than the microhardness of No. Ⅰunder different technology. Green strips could not be sintered in vacuum. Sintered in argon the green strips could not realized sintering from 400℃-550℃for 120 min. After sintering at 400℃-550℃, recrystal grains appeared in powder particles, and particle growing could be observed on some particle boundaries. The strips sintered at 550℃for 120 min could be deformed seriously, and the largest deformation was 50%. The strips being deformed could be sintered successfully at 600℃for 60 min, and with the increase of deformation, the strips could be sintered better. During sintering, Mg and Zn, and Mg and Al occurred phase transformation after which liquid phase appeared. The phase transformation were 342.2℃and 440.7℃respectively. After sintering for 180 min, Al and Zn solved into Mg completely. During dropping in temperature, Al precipitated from Mg to form Mg17Al12.