Manganese is usually added into aluminum alloy after smelting and crushing process by using powder metallurgy technology. In the smelting cooling process, high cooling rate will be used so as to avoid the formation of thick Al6Mn phase. As a result, researchers have tried to add MnAl slice or inject manganese powder into aluminum alloy matrix. Research result shows that by using the former method, different components will react with each other and will release heat, thus the solid solution process of manganese can be maintained without using additional equipment as well as the temperature will be kept in low level in the whole process; besides, material performance will not largely depend on manganese particle size. While by using the latter method, as the manganese metal powder will be injected into aluminum alloy matrix by jet stream, additional equipment will be used. In addition, by using this method, it will have longer process cycle as well as the operating temperature will be obviously higher than the former method. Meanwhile, it has been found that no matter the particle size of manganese powder is larger or smaller than the optimum particle size, they all will have bad influence on material performance.
Al-Mn alloy is a kind of commonly used aluminum alloy, which is composed by two phases: α solid solution and Al6Mn intermetallic compound. Intermetallic compound will have large influence on the mechanical property of alloys. With the increasing of compound content, the yield stress and fatigue resistance of alloys will obviously increase, while the ductility will reduce (especially under low temperature). By adding a small amount of chrome into Al-Mn alloy, the performance of alloy will have significant change. Researchers also have studied the relationship between the mechanical property of Al-(6~8)%Mn-(1~3)%Cr and the composition. Result shows that if the content of Mn and Cr is higher than 8.8 percent, the enhancement degree of alloy will obviously increase due to precipitation. Al-7Mn-3Cr alloy has best strengthening effect, in which the tensile strength can reach 480MPa and the ductility can reach 7 percent. When the chrome content reduces, Al-Mn alloy will precipitate Al6Mn, the second phase; when the chrome content increases, Al7Cr phase will generate. After the heat treatment of hot extrusion alloy samples, G phase will generate, which is the so called (Mn,Cr)Al12 phase. Second phase will have significance influence on the microstructure of alloy and mechanical property. Besides, by adding silicon into Al-Mn alloy, it also will achieve good effects. Researchers also have prepared Al-12.6Mn-4.8Si by using rapid solidification technology. After annealing treatment at 350 degrees Celsius for 100h, the microstructure of Al-12.6Mn-4.8Si samples is still very stable as well as the strength and ductility also keep unchanged. From room temperature to 380 degrees Celsius, the tensile strength will reduce from 465MPa to 115MPa and the ductility will increase from 6 percent to 12 percent; when the temperature rises to 425 degrees Celsius, the ductility will further increase to 30 percent. Meanwhile, the strength and plasticity of alloy will depend on the strain rate. This is because under high strain rate, the strength and plasticity will increase to some degree. The creep test results show that in the range of test temperature, the creep activation energy will be in the range of 100-230 kJ/mol as well as the stress exponent will be in the range of 3-5. High strength AlMnCe alloy that made by powder metallurgy method will have higher wear resistance than the traditional alloy. Al90Mn8Ce2 alloy that made by isostatic pressing under 753-793K and 1.2GPa will have highest compression strength and hardness, which will respectively reach 900MPa and 26HRC. The increasing of strength will depend on the fine grains of alloy and second phase strengthening; researches also show that Al90Mn8Ce2 alloy has good wear resistance. For example, under 773K, the wear resistance of alloy is 3 times higher than normal A355 aluminum alloy. It also has been found that Al6Mn, Al4Ce, Al2O3 and other second phase hard particles will have positive effect on improving the wear resistance of alloys.
Manganese, being served as the main component and additive of powder metallurgy material, will have important effect on improving material performance and developing new materials; besides, as manganese has abundant resource as well as is very cheap, it will have important significance no matter in scientific theory or in production practice by studying and developing the application of manganese. With the expansion of market demand and development of material science, the application prospect of manganese will become wider and wider.
However, the characteristic of manganese has limited the expansion application. This is because manganese is easy to oxidize, while the oxides are very difficult to reduce. In powder metallurgy production, the oxidation of manganese could be regarded as a tough problem. With the development of powder preparation and sintering technology, manganese oxidation condition has been reduced to some degree, but has not been thoroughly solved yet. Therefore, in order to expand the application of manganese, we should strengthen researches on this aspect and try our best to find proper solutions.
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