Makoto Sugamata

Structures and mechanical properties of rapidly solidified Mg-Y based alloys

Abstract Mg-Y based alloys with or without ternary additions of Ca and Zn were rapidly solidified and consolidated into P/M materials by hot extrusion. Ternary alloying additions were 3 ma.% Ca for the Mg-5ma.%Y alloy and 2 ma.% Zn for the Mg-10ma.%Y alloy. Consolidation of the flakes was carried out by cold pressing and hot extrusion. In as rapidly solidified flakes of the Mg-Y binary alloys, extended solid solution of Y was obtained in the Mg matrix. But, fine lamellar structures, the spacing of which was approximately 400 nm, were observed in rapidly solidified flakes of the ternary alloys. Rapidly solidified flakes containing 10 ma.% Y showed hardness increases after heating at 473 K presumably due to precipitation of metastable β″ phase. After consolidation, a fine dispersion of intermetallic compounds was observed in all extruded P/M materials. Those compounds consisted of Mg24Y5 in binary alloys, and Mg24Y5, Mg2Ca or Mg12YZn in the ternary alloys. As-extruded P/M materials of Mg-10ma.%Y and Mg-10ma.%Y-2ma.%Zn alloys showed no remarkable softening after annealing at 573 K. The Mg-10ma.%Y-2ma.%Zn alloy showed the highest tensile strength of 520 MPa at room temperature and 440 MPa at 473 K. However, the tensile strength of all the P/M materials dropped below 80 MPa at 573 K.

Structural features of mechanically alloyed Al–PbO and Al–PbO–WO3 composites

Abstract Mechanical alloying, cold compression and hot extrusion were used to prepare Al–PbO–WO 3 and Al–PbO composites. The as-extruded and annealed samples were examined by means of transmission electron microscopy and X-ray analysis. Heavily deformed matrix containing very fine particles of basic components and some remaining Al-grains were observed in the as-extruded materials. Because of high affinity of oxygen to aluminum the heavily deformed matrix was chemically unstable on annealing at high temperatures. A thin Al-oxide layer around W-rich particles resulted from chemical reaction between aluminum matrix and WO 3 -particles in samples annealed for 1–2 h at 873 K. Reduction of PbO-particles within the Al-matrix was found to result in growth of cavities and coarsening of Pb-particles within pores. Colonies of very fine oxides within pores and Pb-particles located close to neighboring Al-matrix were often observed in annealed samples.

Effect of annealing temperature on the structure and mechanical properties of mechanically alloyed AlMg–Nb2O5 and AlMg–ZrSi2 composites

Mechanical alloying and hot extrusion method were used for manufacturing AlMg‐based composites reinforced with addition of niobium oxide (Nb2O5) and zirconium silicide (ZrSi2) particles. High mechanical properties of the materials were found to result from heavily refined structure of composites. It was found that the composite structure was transformed at high temperature as a result of irreversible chemical reaction between disperse reinforcements and surrounding matrix. Chemical reaction for AlMg–Nb2O5 composite results in a growth of intermetallic grains of Al3Nb type and very fine oxides particles of 5–20 nm in diameter. In the annealed AlMg–ZrSi2 composite, new grains of Al3Zr, Mg2Si and Al(Mg)O are formed as a result of zirconium silicide decomposition. Hot compression tests were performed at constant true strain rate of 5.10−3 s−1 within the temperature range of 293–823 K. The high flow stress values are attributed to highly refined structure of the materials that essentially did not coarsen in spite of high deformation temperature.

High-strength and thermally stable Al – CeO2 composite produced by means of mechanical alloying

Abstract The effect of temperature on both mechanical and structural features of a new Al-based metallic composite reinforced with fine CeO2 particles was the primary objective of the research work. Mechanically alloyed Al – CeO2 composite was manufactured from high purity Al and CeO2 powders. The powders were milled under argon atmosphere and then consolidated using hot pressing, vacuum degassing and hot extrusion methods. Hot compression tests revealed high mechanical properties of the material, which were ascribed to the very fine-grained structure of the composite. Transmission electron microscopy observations were performed on as-extruded material and samples annealed at 773 K. It was found that the composite structure is relatively stable at 773 K in comparison to Al-based composites reinforced with other heavy-metal oxides reported in literature.

Microstructure and Mechanical Properties of Rapidly Solidified Al-Fe-Ni-Mg Alloys

Rapid solidification (RS) combined with following mechanical consolidation of RS powders is considered as a valuable commercial method for the production of a wide range of metallic materials having fine-grained structures. Reported research results for various alloys demonstrate better compositional homogeneity, smaller grain size and relatively fine precipitates distributed homogenously in RS alloys than that for the materials produced by conventional metallurgical processing. The effect of rapid solidification on the microstructure and mechanical properties of selected Al-Fe-Ni-Mg alloys have been investigated. The basic item of the research work was obtaining aluminum PM materials strengthened by highly-dispersed transition metal compounds and aluminum-magnesium solid solution. Rapid solidification (RS) of Al-4Fe-4Ni and Al-4Fe-4Ni-5Mg alloys was performed by means of gas atomizing of the molten alloy and the spray deposition on the rotating water-cooled copper roll. Using typical powder metallurgy (PM) methods, i.e. cold pressing, vacuum degassing and hot extrusion, the RS-flakes were consolidated to the bulk PMmaterials. For comparison purposes, the conventionally cast and hot extruded Al-4Fe-4Ni and Al-4Fe-4Ni-5Mg alloys were studied as well. Mechanical properties of as-extruded materials were examined by compression tests performed at 293 K – 873 K. It was found that relatively high strength of as-extruded PM materials was accompanied by high ductility of samples deformed by hot compression test. Structural observations confirmed beneficial influence of rapid solidification on effective refining of intermetallic compounds, although some inhomogeneity of fine precipitates distribution was observed. Nevertheless, it was considered that an effective increase of the microhardness and strength of tested RS materials mostly result from achieved dispersion of structural components and can be intensified by solid solution hardening due to Mg-addition.

Structure and properties of P/M material of AlMg - SiO2 system processed by mechanical alloying

New methods of material processing have been actively pursued in recent years in an attempt to extend current materials performance. Of particular interest are the powder metallurgy (P/M) techniques of mechanical alloying (MA). The MA process is generally used to create the materials with unique properties which give the material a wide spectrum of possible advanced applications. Light - metal based mechanically alloyed composites strengthened by heavy metal oxides addition (MeO) [1] have been examined according to bilateral research cooperation between Nihon University, Tokyo and AGH — University of Science and Technology.

Structural and Mechanical Features of Rapidly Solidified Al-2Fe-2Ni-5Mg Alloy

Rapid solidification (RS) of Al-2Fe-2Ni-5Mg alloy and following mechanical consolidation of powders by means of powder metallurgy (PM) methods was used with success to produce a bulk RS-material. RS powders were manufactured using an inert gas atomizing of the molten alloy and the spray deposition on the rotating water-cooled copper roll. Rods of 7 mm in diameter were received by means of the cold pressing of the flakes, vacuum degassing and hot extrusion method. For comparison purposes, the conventionally casted and hot extruded Al-2Fe-2Ni-5Mg alloy was tested as well. Mechanical properties of as-extruded materials were examined at 293 K – 873 K by compression tests performed at constant true strain rate of 5·10-3[s-1]. It was found that relatively high strength of as-extruded RS/PM material was accompanied by the high ductility of the samples deformed by hot compression tests. It was noticed that the most effective solution strengthening due to particles refining was observed at low deformation temperatures. Rising the test temperatures above ~ 420 K, was found to result in reduction of the flow stress to the values received for the industrial material (IM).The formation of coarse primary intermetallic compounds, which is typical for IM material, was effectively reduced for RS material. However some inhomogeneity of fine precipitates distribution in RS/PM material was observed. Nevertheless, it was considered that both solid solution hardening due to Mg addition and the dispersion strengthening due to refining of intermetallic compounds substantially increase the mechanical properties of the RS/PM material.

Microstructure and mechanical properties of AA7039+20%SiC W composite.

Hot deformation tests were performed on an AA7039‐matrix composite reinforced with a 20% addition of SiC whiskers. The flow stress maximum was reduced with deformation temperature from 640 MPa to ∼8 MPa at 293 K and 823 K, respectively. TEM observations, performed on as deformed samples, revealed a highly recovered substructure of the matrix and a striated structure of the whiskers. The fringes, which are perpendicular to the whiskers’ longitudinal axis, were ascribed to nano‐sized twins and stacking faults formed during the crystal growth rather than to some effects of the deformation process.

Superplastic Properties of Rapidly Solidified Mg-Al-Zn Alloys

With a purpose of obtaining materials of high specific strength at room temperature and superplastic elongation at elevated temperatures, Mg-Al-Zn ternary alloys containing 1 to 10 mass%Al and 5 to 12mass%Zn were rapidly solidified by gas atomizing and subsequent splat quenching. The rapidly solidified flakes were consolidated to the P/M materials by hot extrusion at 573K. The obtained P/M materials showed finer dispersion of the second phase particles than the I/M counterparts. The hardness and tensile strength of the P/M and I/M materials at room temperature increased linearly in parallel to each other with increasing Al+Zn content in atomic%. The highest tensile strength of 447MPa at room temperature was obtained for rapidly solidified Mg-8mass%Al-12mass%Zn. The decreases in tensile strength and increase in elongation with rising test temperature were more remarkable in the P/M materials than in the I/M materials. At 573K, tensile strength of the P/M materials decreased to below 20MPa and elongation increased to above 100% for a wide range of tensile strain rate. The highest elongation above 900% was observed at 573K for the Mg-10mass% -5mass%Zn P/M material at an initial strain rate of 0.02/s.

Mechanical and Structural Characterization of Rapidly Solidified Al-Fe-Mg Alloys

Series of experiments on a series of Al-Fe-Mg alloys were performed to determine the effect of rapid solidification (RS) on the material strengthening, which result from the refining of thegrain size and intermetallic compound. Additionally, an enhancement of the material strengthening due to magnesium addition was also observed. Manufacture of RS Al-Fe-Mg alloys combined a spraydeposition of the molten alloy on the rotating water-cooled copper roll and plastic consolidation bymeans of powders pressing and hot extrusion methods. The results suggest that the rapid solidification provides an effective method of microstructure refinement and, in combination with solid solutionhardening due to Mg, leads to significant improvement of mechanical properties of Al-Fe-Mg based alloys.