Magnesium Alloy Chips Research Articles

Methods for Prevention of Ignition during Machining of Magnesium Alloys

Magnesium alloys have been increasingly used in automotive and aerospace components and in portable microelectronic devices due to their “ultralightness” and high specific strength. Machining is an important method used to process magnesium alloys. The advantages of machining over other processing methods such as die casting include reduction in power consumption and excellent surface finish. However, the ignition of chips presents a dangerous problem during machining. This problem has attracted considerable research interests. Though coolants can be used effectively to prevent ignition, the pollution of environment and reclamation of chips can not be resolved easily. Therefore, one better approach is to control the machining parameters for minimizing ignition hazard of magnesium alloy chips during dry machining. A systematic study was conducted for a few different magnesium alloys (including AM50A and AZ91D) to understand effect of cutting parameters (cutting speed, feedrate and depth of cut) on ignition of chips during face milling. It is interesting to find that for any fixed cut depth ignition in the forms of sparks, flares or ring of fire occurs only in the moderate cutting speeds and feedrates and can thus be easily prevented by adopting either higher or lower cutting speeds or feedrates. Chips produced in different machining conditions were collected and their morphology was analyzed to understand mechanisms of ignition.

Microstructure and mechanical properties of AZ31B magnesium alloy prepared by solid-state recycling process from chips

AZ31B magnesium alloy chips were recycled by three solid-state recycling processes including cold-pressing, hot-pressing followed by hot extrusion and double extrusion. Microstructure and mechanical properties of the recycled specimens and reference specimens were compared. For the recycled specimen by cold-pressing, the grains are refined to a large extent during hot extrusion due to the presence of twins and high density dislocation. The recycled specimens by hot-pressing and double extrusion do not exhibit finer grain than that the recycled specimen by cold-pressing. Consequently, higher ultimate tensile strength of the recycled specimen by hot-pressing and double extrusion is not achieved. For hot pressing process, more compact billet lowers the porosity in recycled material, so elongation to failure of the recycled specimen increases. The recycled specimen fabricated by double extrusion process shows slightly higher elongation than the reference specimen. The second extrusion makes the oxides further crush and distribute more dispersedly, and minimizes porosity, which is responsible for the improved ductility.

押出し固化成形を利用したマグネシウム合金切削屑の新再生法

押出し固化成形を利用したマグネシウム合金切削屑の新再生法

Microstructure and mechanical properties of AZ31B magnesium alloy recycled by solid-state process from different size chips

AZ31B magnesium alloy chips of different size were recycled by hot extruding. Mechanical properties and microstructure of the recycled specimens and reference specimen were investigated. Amounts of oxide in recycled materials were estimated. Almost all the recycled specimens exhibit higher strength than reference specimens, this is mainly attributed to grain refinement strengthening whereas particle-dispersion strengthening has few effect. The strength of recycled specimen increases with increasing of total surface area of chips because of different grain size. Recycled specimens show inferior ductility than reference specimens and recycled specimens with medium surface area of chips possess highest elongation. Grain size, oxide amount and density of billet have an effect on the elongation of recycled materials.

W03(3) マグネシウム合金チップを利用した生産技術 : 押出し加工(W03 環境と共生する軽金属(Al, Mg, Ti)材料の有効利用,ワークショップ,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

W03(3) マグネシウム合金チップを利用した生産技術 : 押出し加工(W03 環境と共生する軽金属(Al, Mg, Ti)材料の有効利用,ワークショップ,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Effect of chip size on mechanical property and microstructure of AZ91D magnesium alloy prepared by solid state recycling

In this study, different kinds of AZ91D magnesium alloy chips were prepared by solid state recycling. Mechanical properties and microstructures of the recycled specimens were investigated. Various microstructural analyses were performed using the techniques of optical microscopy, scanning electron microscopy and oxygen-nitrogen analysis. Microstructural observations revealed that all the recycled specimens consisted of fine grains due to dynamic recrystallization. The oxide precipitate content is closely related to the recycled chip size. Accumulated oxygen concentration linearly increases with the total surface area of the machined chips in the recycled specimens. Ambient oxide in the recycled specimen contributes to a higher ultimate tensile strength and a higher elongation to failure; however, excessive oxide in the recycled specimen may adversely affect the elongation to failure.

Mechanical properties of continuously consolidated Mg96Zn2Y2 magnesium alloy chips

The authors examined the properties of Mg96Zn2Y2 alloy bars made through continuous consolidation of chip using a newly developed single screw extrusion machine designed for magnesium alloy chip. Surface conditions as well as microstructure of the consolidated Mg96Zn2Y2 alloy varied depending on the die conditions. With a die inner diameter of 49 mm and die temperature of 723 K, severe plastic deformation in the die produced a fine-grain microstructure in the consolidated Mg96Zn2Y2 alloy bar. The compounds such as Mg12YZn and Mg3Y2Zn3 in the bar were also dispersed finely. Owing to its randomized crystal orientation, a secondary extruded bar made from the consolidated Mg96Zn2Y2 alloy bar showed a higher ductility than that of ingot-extruded bar. The fine-grain consolidated Mg96Zn2Y2 alloy bar exhibited an elongation of 308% at 723 K. Furthermore, the deformation characteristics were examined with the consolidated Mg96Zn2Y2 alloy bar for the purpose of determining its suitability as hot-processing material billets. The fine-grain consolidated Mg96Zn2Y2 alloy bar was compressed without cracking up to 623 K while Mg96Zn2Y2 ingot cracked. It was found that smaller grain diameter made the m-value higher.

Fracture Analysis and Mechanical Property of AZ91D Magnesium Alloy Chips Prepared by Solid State Recycling

AZ91D magnesium alloy is prepared by hot extrusion of recycled machined chips and its fractures and mechanical properties are investigated at various extrusion conditions. Cold-press is employed to prepare extrusion billets of AZ91D magnesium alloy chips, and then the billets are hot extruded at 573K-723K with an extrusion ratio of 11:1. The results show that tensile strength and elongation of the extrusion magnesium alloy with the extrusion temperature of 673K and the extrusion rate of 0.08mm/s can reach 380MPa and 6%, respectively. Fracture surface presents a mix mechanism of dimple-like fracture and gliding fracture. Due to grain refinement by cold-press and hot extrusion, mechanical properties of extruded rods are much higher than those of as-cast AZ91D magnesium alloy. Also, much lower energy consumption is necessary for this recycling compared to the conventional casting process. Solid state recycling is an efficient method for magnesium alloy chips recycling.

Mechanical Alloying of Powder Mixture of Magnesium Alloy Chips and Aluminum

Mechanical Alloying of Powder Mixture of Magnesium Alloy Chips and Aluminum

Consolidation of machined magnesium alloy chips by hot extrusion utilizing superplastic flow

An examination of consolidation conditions by hot extrusion of AZ31 magnesium alloy machined chips was conducted to enhance the bonding of individual chips, in order to improve the mechanical properties. Hot extrusions were carried out in the superplastic and non-superplastic region. Microstructural observations revealed that grain refinement was attained by extruding machined chips, and the grain sizes of the chip-extruded materials were smaller than 5 μm. The interfaces of individual chips of extruded materials were not identified when the chips were extruded in the superplastic region. The ultimate tensile strength was about 300 MPa and elongation-to-failure was about 10% for chip-extruded materials that were extruded in the superplastic region. These materials were comparable with the as-received alloy with respect to the room temperature strength, although the ductility was reduced to half. It was confirmed that chip consolidation utilizing superplastic flow is useful to enhance the bonding of individual grains.

Superplastizität von Magnesiumlegierungen

Trotz des in der Industrie in den letzten Jahren stark gestiegenen Interesses an extrem leichten Magnesiumkonstruktionswerkstoffen ist die breite industrielle Nutzung vor allem durch die begrenzte Kaltumformbarkeit als Folge der hexagonalen Gitterstruktur bisher stark eingeschränkt. Lösungswege zeigt in diesem Zusammenhang die superplastische Umformung von Magnesiumlegierungen auf, welche im Vergleich zu anderen Werkstoffgruppen sowohl in metallurgischer, werkstoffwissenschaftlicher aber auch verarbeitungstechnischer Hinsicht bisher nur eingeschränkt untersucht und zielgerichtet optimiert worden. Ein sehr erfolgversprechender Schritt stellt in diesem Zusammenhang die einfache und recyclingfreundliche Herstellung von Magnesiumlegierungen mit besonders feiner Mikrostruktur durch mechanisches Umformen von Magnesiumspänen dar. Nach einer kurzen Vorstellung der theoretischen Grundlagen und Methoden zur Ermittlung der superplastischen Eigenschaften werden die stark verbesserten Materialeigenschaften anhand von Ergebnissen verschiedener Dehngeschwindigkeitswechselversuche für diverse Magnesiumlegierungen nachgewiesen. Superplasticity of Magnesium Based Alloys In despite of the increasing interest of the industry in extremely lightweight materials during the last years an intensive industrial use of those materials due to the their restricted cold-workabilit caused by the hexagonal lattice is still very limited. Considering this limitation a solution is provided by the superplastic forming of magnesium based alloys which in contrast to other types of materials is neither metallurgically developed nor process optimized. A very promissing step is the cost-saving and recycling-favorable production of a very fine grained microstructure through the use of extruded magnesium alloy chips. After a short introduction of the theoretical basics and methods to quantify the superplastic behavior the results of velocity change test with different magnesium alloys will be shown.

Extrusion ratio and mechanical properties of extruded machined magnesium alloy chips: K. Higashi et al. (University of Osaka Prefecture, Sakai, Japan.) J. Japan Soc. Powder and Powder Metallurgy, vol 42, no 3, 1995, 373–377. (In Japanese.)

The corrosion behaviors of pure Mg and AZ31 Mg alloy recycled by a solid-state process were investigated by salt (5 wt.% NaCl solution) immersion tests, and were compared with those of an ingot reference and an extrusion reference subjected to the same deformation history. The recycled specimen possessed superior corrosion resistance compared with the reference ones, contrary to anticipated apprehension. The enhancement of corrosion resistance for the recycled specimens was attributed to the presence of dense oxide contaminants which were distributed parallel to the extrusion direction. The addition of Al accelerated the enhancement of corrosion resistance by solid-state recycling. This suggests that the capacity of the oxides as corrosion barriers depends their elemental content.

半溶融撹はんしたＡＺ９１Ｄマグネシウム合金チップ材の流動性および加圧成形後の機械的性質

Stir-cast AZ91D magnesium alloy chips were reheated at semi-solid state and press-formed by employing a squeezecasting machine at semi-solid temperature. The structures and tensile properties of the formed specimen were investigated. Stir-cast chips show good fluidity and have little defects because of fine and spherical magnesium solid solution with a large amount of liquid phase. Tensile properties of the semi-solid press-formed specimen are, therefore, improved by the T6 heat treatment. The eutectic microstructure becomes finely by the rapid cooling, resulting in the increased 0.2% proof strength which exceeds the JIS-specified value. But tensile strength and elongation are less than the JIS-specified values. This is caused by oxide layer formed on the slurry surface during stirring.