Milling of magnesium powders without additives (original) (raw)
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Development of Mg-Alloy by Powder Metallurgy Method and Its Characterization
Powder Metallurgy and Metal Ceramics, 2019
In the present research work, an attempt has been made to make Mg-alloy specimen by powder metallurgy. Due to sensitivity of the material, a proper selection of sintering atmosphere has been made. Mg powder along with other powders has been blended with a high energy ball mill. In this work, the effect of input parameters, such as compaction pressure, sintering temperature and sintering time was investigated on porosity, microhardness and dimensional change. The compaction pressure and sintering temperature play a significant role in the porosity and microhardness. Increasing the compaction pressure plays a positive role in the microhardness. The maximum value of the porosity in the present work was up to 37.41%. The dimensional expansion after sintering varies from 2 to 4.3%. The results of the porosity and microhardness were verified by scanning electron microscopy and X-ray diffraction.
Fabrication of Magnesium Alloy from a Pre-Alloyed Powder Using Hot Die Compaction Process
The International Conference on Applied Mechanics and Mechanical Engineering, 2008
AZ91D magnesium alloy was fabricated by using pre-alloyed powder compressed without any binder agent at 280 o C under the compaction pressure of 200 MPa at different time intervals of 2, 4, 6, 8 and 10 hours. Some of the compressed samples were then undergone a sintering process at temperature of 450 o C for 3 and 6 hours. Furnace cooling was performed after the sintering. Microstructure and hardness of each specimen were investigated. The microstructures observation and hardness investigation of the as-hot compacted and sintered samples were then compared. The results showed that microstructure transformation occurred due to the hot compaction and the sintering for 3 and 6 hours. The as-hot compacted samples showed a grown globular precipitates (β phase, Mg 17 Al 12) distributed uniformly in grains. However, after sintering process, lamellar precipitates took place and dominated the grains. The as-hot compacted sample showed higher hardness value compared to the 3 hours and 6 hours sintered samples.
Novel approaches to grain refinement of magnesium alloys
Grain refinement of cast metals through inoculation has been one of the most favourable approaches in the industry due to its convenience, low cost and reproducible good results in obtaining fine equiaxed as-cast microstructures. Grain refinement is also considered one of the most effective approaches to simultaneously improve castability, strength, ductility and formability of metals. Since the 1990's, Mg has been one of the most important structural materials, particularly in the automotive industry, due to its abundance in the earth's crust, lightness and good castability. However, as-cast Mg is usually associated with low strength, ductility and creep resistance. In the last couple of decades, grain refinement of Mg alloys has been an active research topic, because achieving finer grains is found to be increasing both strength and ductility of the alloys. So far, it is believed that grain refinement by inoculation can be achieved through restricting the grains growth by controlling the constitutional undercooling during solidification or through increasing the nucleation rate in the melt or both. However, a number of important details in the grain refinement mechanism are still unknown and there has not been a unique model found in the literature that can fully satisfy all experimental findings. In addition, most of the developed grain refiners are not as effective as zirconium which is considered the most effective grain refiner for Mg so far; but it does not work with Mg-Al alloys which form the majority of commercially used Mg alloys. In order to design a new grain refiner, growth restriction factors (Q-values) of a number of solutes that have not been found in the literature were calculated in binary Mg alloys. Following that, calculations using the edge-to-edge crystallographic matching (E2EM) model predicted FCC-CaO as an effective nucleant for the HCP-Mg. Casting experiments were then undertaken through addition of various amounts of CaO into the Mg melts. As-cast optical micrographs showed dramatic reduction in grains size with CaO particles addition. At 0.3 wt.% CaO addition level, columnar to equiaxed (CTE) transition of Mg alloys was firstly observed. Further CaO addition led to further grain refinement. Through SEM analysis CaO particles were spotted at the centres of the grains, which indicated that CaO particles can successfully nucleate Mg grains. In addition, Ca solute was introduced into the melt through decomposition of some CaO particles, which further improved the grain refinement efficiency. Addition of CaO into Mg-Ca and Mg-Zn alloys led to even more grain refinement; but grain coarsening was obtained in Mg-Al-CaO alloys. The effect of CaO on the mechanical properties of Mg alloys was then studied through preparing two groups of samples (Mg-Ca and Mg-CaO based alloys). Tensile and hardness results showed that both sample groups were strengthened. However, the grain refinement strengthening component was higher in Mg-CaO base alloys.
Grain refinement of commercial purity Magnesium processed by Ecap (Equal Channel Angular Pressing)
Materials Research, 2012
Grain refinement in magnesium is evaluated in the present paper. Equal Channel Angular Pressing is used to process commercially pure magnesium. Processing was carried out at 523 K which is lower than the temperature used in other papers on the literature. The grain structure was evaluated throughout the deformation zone. The low processing temperature prevents significant grain growth. The evolution of the grain structure is compared to a recent model for mechanism of grain refinement in magnesium. The present results confirm the validity of the model.
A Review on Wrought Magnesium Alloys Processed By Equal Channel Angular Pressing
Magnesium and its alloys withsevere plastic deformation (SPD) techniques are more attractive asstructural parts in many industrial applications because of their advantages. In this paper, the importance of wrought magnesium alloys with their applications to accomplish the essential development of components is reviewed. In addition, the different approaches of equal channel angular pressing (ECAP)process for refining the grain size to achieve the ultrafine grained material on the bulk metals are discussed. Recent developments in the ECAP process are outlined clearly with their importance to overcome many complexities. Various factors like processing temperature of a specimen, die geometry, ram speed, back pressure and processing routes influencing during ECAP process of wrought magnesium alloys at different conditions such as channel angle and corner or outer arc angle are discussed. Finally, the properties of ECAP processed wrought alloys are outlined for improving the microstructure in structural parts.
Journal of Materials Research and Technology, 2013
Pressing (ECAP) at 523 K. The grain structure was evaluated at the region near the intersection between the channels of the die. Compression test workpieces were machined from the as-received material and the material processed by ECAP. These workpieces were tested at room temperature. The results show the grain structure is refined in the intersection between the channels. The ECAP processed material displays higher strength and reduced surface bulging due to the refined structure. The plastic flow during compression of the ECAP processing material concentrates along bands of refined grains.
Metallurgical and Materials Transactions A, 2013
This paper builds on the ''Grain Refinement of Mg Alloys'' published in 2005 and reviews the grain refinement research on Mg alloys that has been undertaken since then with an emphasis on the theoretical and analytical methods that have been developed. Consideration of recent research results and current theoretical knowledge has highlighted two important factors that affect an alloy's as-cast grain size. The first factor applies to commercial Mg-Al alloys where it is concluded that impurity and minor elements such as Fe and Mn have a substantially negative impact on grain size because, in combination with Al, intermetallic phases can be formed that tend to poison the more potent native or deliberately added nucleant particles present in the melt. This factor appears to explain the contradictory experimental outcomes reported in the literature and suggests that the search for a more potent and reliable grain refining technology may need to take a different approach. The second factor applies to all alloys and is related to the role of constitutional supercooling which, on the one hand, promotes grain nucleation and, on the other hand, forms a nucleation-free zone preventing further nucleation within this zone, consequently limiting the grain refinement achievable, particularly in low solute-containing alloys. Strategies to reduce the negative impact of these two factors are discussed. Further, the Interdependence model has been shown to apply to a broad range of casting methods from slow cooling gravity die casting to fast cooling high pressure die casting and dynamic methods such as ultrasonic treatment.
Review on Magnesium Alloy Processing
2020
Demand to design engineering components with lightweight materials is a big challenge for the twenty-first-century engineer. Many researchers of the world have been trying hard to innovate new lightweight and energy-efficient alloy materials to replace steel and other metallic alloys. So far magnesium alloys are found fit for the purpose. But its alloying process is a little bit tough as molten magnesium is more prone to oxidation. Therefore, to improve its corrosion resistance and mechanical properties, researchers have been trying to establish new alloy systems in order to fulfill requirements from different industries especially automobile, aerospace, and health sector. Magnesium melting techniques, different Mg–alloy systems, and effect of alloying elements on the alloy have been discussed in this paper.