Junichi Kaneko

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.

Structures and properties of rapidly solidified MgCa based alloys

Abstract With the aim of developing new light weight and high strength materials, rapidly solidified flakes of MgCa based alloys with or without ternary additions such as Zn, Si and Ce were produced by atomizing the alloy melt and subsequent splat-quenching on a water-cooled copper roll. The flakes were consolidated by hot extrusion. Metallographic structures and constituent phases were examined for both rapidly solidified flakes and powder metallurgical (PM) materials, and mechanical properties were evaluated for PM materials. The rapidly solidified flakes show fine dendritic cell structures with the cell size ranging from 0.2 to 2 μm. Hardness increased on heating the flakes of MgCa binary alloys at 373–473 K, presumably due to precipitation of Mg2Ca from extended solid solution of Ca in Mg. No such hardness increase is observed in the ternary alloys. After consolidation, fine grained structures with fine dispersions of intermetallic compounds are observed in all extruded PM materials. The highest tensile strength of 483 MPa was obtained in Mg-5mass%Ca-5mass%Zn PM material with 2% tensile elongation. The tensile strength decreases and elongation increases significantly with rising test temperature. At elevated temperatures. A PM material of MgCa binary alloys shows lower tensile strength than alloys with ternary additions. Nearly superplastic elongation of 200% is observed in Mg-5mass%Ca-5mass%Zn PM materials 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.

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.

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.

Extrusion of rapidly solidified 6061 + 26 wt% Si alloy

Due to low thermal expansion coefficient, high strength to weight ratio as well as high wear and corrosion resistance, high silicon aluminum alloys are commonly used in aerospace, automobile industry and many other practical applications [1]. The most common aluminum foundry alloys contain 5 – 12 wt % silicon. Higher content of silicon is not useful for commonly produced as-cast materials because of embrittlement effect resulted from the coarse primary silicon development. The most of mechanical properties of castings are determined by the silicon and eutectic structure morphology [2]. Some refining of the structure can be achieved by means of mechanical mold vibrations at high enough amplitudes [3], modifications with alkali or rare earth metals [4] and also by increasing the cooling rate during casting procedures [2]. However, the most effective refining of Al – Si alloy structure can be achieved due to rapid solidification (RS) combined with powder metallurgy (P/M) methods. Experiments described bellow were performed on RS powder of 6061 + 26 wt% Si alloy that was mechanically consolidated by vacuum hot compression and extrusion procedures. The RS powder was produced by air spray atomization at Toyo Aluminum Company. Chemical composition of the alloy is shown in Table 1. Table 1. Chemical composition of 6061+26%Si alloy Element Si Mg Cu Fe Cr Zn Al wt.% 26.0 0.69 0.16 0.21 0.11 0.11 in balance

Mechanically Alloyed P/M Composites of Al-Mg-Silicide and Al-Mg-Oxide Systems

Al-Mg alloy powder was mechanically alloyed with addition of metal silicide and metal oxide powders. The metal silicide powders of CrSi 2 , TiSi 2 , ZrSi 2 , WSi 2 , MoSi 2 and metal oxide powders of B 2 O 3 , Sc 2 O 3 , TiO 2 , SrO 2 , CeO 2 were added to Al-8at%Mg alloy, and mechanical alloying (MA) treatment was conducted by using an attritor-type ball mill. Solid state reaction during MA and subsequent heating was studied. The MA powders were consolidated to the P/M composites by vacuum hot pressing and hot extrusion, and their structures and mechanical properties were examined. It was shown that all added oxides but TiO 2 were decomposed during heating of the MA powders, and aluminide compounds and spinel (MgAl 2 O 4 ) were formed within the Al-Mg alloy matrix. All added silicides were only partially decomposed and Mg 2 Si was formed during heating of the extruded P/M composites. Structural coarsening during heating of the Al-Mg-silicide system was more pronounced than that in the Al-Mg-oxide system. The P/M composites of Al-Mg-oxide system showed higher hardness than those of the Al-Mg-silicide system. The highest hardness of 237HV was observed for Al-Mg-B 2 O 3 P/M composite. The P/M composite of Al-Mg-CrSi 2 showed the highest tensile strength of 578MPa. Although high tensile strength was obtained, Al-Mg-silicide composites showed poor ductility.

Creep and Creep Rupture of FSW Joints of 5052 Aluminium Alloy Plates

Creep and creep rupture tests were carried out for friction-stir-welded (FSW) joints of 5052 aluminum alloy plates at temperatures between 573 and 723 K. The results were compared with those of the base metal. 5052-O plates of 20 mm in thickness were joined by FSW and round bar creep specimens were machined out of the welded plates. Tensile tests were also conducted at RT, 623 and 723K for both FSW joints and base metal. The tensile strength of the joints was almost the same as that of the base metal at room and elevated temperatures. However, the FSW joints showed appreciably higher minimum creep rate and shorter rupture time than the base metal at all the tested temperatures and initial creep stresses. Creep rupture of the joints always occurred within the plastically stirred zone with lower contraction of cross-sectional area. Thus, FSW joints of 5052 alloy plates showed lower creep strength than the base metal.