Jun Kusui

Effect of Mn Intermetallic Particle on Microstructure Development of P/M Al-Zn-Mg-Cu-Mn Alloy

The Mesoalite alloy is formed using rapidly solidified powder metallurgy (RS-P/M) by hot extruding the RS powder produced by the atomization method. Meso20 is a Mesoalite alloy with a chemical composition of Al-9.5Zn3Mg-1.5Cu-4Mn-0.04Ag (mass%). Meso20 contains fine grains and precipitated intermetallic Mn compounds, and has a tensile strength of 910 MPa. During hot extrusion, dynamic recrystallization occurs and the fine grains develop. During heat treatment of Meso20, rod-like and granular Mn intermetallic compounds precipitate. The rod-like compounds are about 1 Ìm in length and the granular compounds are about 1 Ìm in diameter. X-ray diffraction measurement, transmission electron microscopy and energy dispersive X-ray (TEM/EDX) analysis and Rietveld analysis revealed the chemical composition of the granular and rod-like Mn intermetallic precipitates to be 86.5Al-10.9Mn-0.4Cu-0.9Zn-1.3Mg and 80.5Al - 10.3Mn-4.2Cu-2.5Zn-2.5Mg (mass%), respectively. The granular and rod-like compounds were identified as the Al6Mn and Q phases, respectively, with both belonging to the space group Cmcm. The lattice constants of Al6Mn were a=0.754 nm, b=0.648 nm c=0.855 nm and those of the Q phase were a=0.765 nm b=2.34 nm c=1.25 nm. Meso10, with a chemical composition of Al-9.5Zn-3Mg-1.5Cu-0.04Ag (mass%), contains no Mn and does not have fine grains, but rather coarse fibrous grains elongated along the extrusion direction. Thus the Mn intermetallic precipitates in Meso20 clearly affect the formation of fine grains. Microstructure development was studied during hot extrusion by observation using high resolution Electron Back Scattering Pattern method. Fine grains were found to develop in areas, which were relatively abundant in granular Mn intermetallic precipitates.

Effect of Deformation Temperature on High Strain Rate Superplastic Properties in PM 2024Al-Fe-Ni Alloys

High strain rate superplastic properties of high strength PM 2024Al-3Fe-5Ni alloys with or without 0.3 mass % Zr addition have been investigated at a wide testing temperature range of 673K- 793K. The alloys were fabricated by an air atomization technique, followed by extrusion at 623 K and warm rolling at 523K. After the warm rolling, these alloys exhibited ultrafine grained matrix structure. Heating rate to the testing temperatures influenced the superplastic properties of the warm rolled alloy sheets remarkably. After the slow heating (0.8K/s) up to the testing temperature, PM 2024Al-3Fe-5Ni alloy showed the relatively low maximum elongation of about 250% (m=0.35) at a strain rate of 3 S - even at 773K, which is very close to the solidus temperature of the matrix alloy. However, in the case of the rapid heating rate (2.6K/s) condition, the superplastic properties were improved remarkably at the temperature range between 713K and 773K, due to the suppression of microstructure coarsening before testing. Therefore, the fine grain structure capable of grain boundary sliding was considered to be always necessary for the high strain rate superplaticity.

Effect of hot-extrusion conditions on mechanical properties and microstructure of P/M Al-Zn-Mg-Cu alloys containing Zr

The effect of extrusion rate and ratio on the Al3Zr induced dynamic recrystallization (DRX) that occurs during hot extrusion of RS-P/M Al-Zn-Mg-Cu-Zr alloys was investigated. An increase in the logarithm of extrusion rate promoted DRX and lead to a monotonic increase in the number of fine grains. Although DRX was also promoted and the grain size reduced by an increase in extrusion ratio from 10 to 20, the DRX behavior hardly changed, even when the extrusion ratio exceeded 20. However, with increasing extrusion ratio, the width of fibrous grain, i.e., the unrecrystallized region, decreased and the tensile strength increased to 879 MPa. When the extrusion rate and ratio exceeded 54 mm/min and 20, respectively, a marked grain coarsening occurred upon solution treatment, and the tensile strength tended to decrease, because of the high dislocation density induced by hot extrusion. By annealing at 563 K before solution treatment, it was possible to prevent grain coarsening, and thus prevent the strength decrease.

Mechanical Properties of Dispersion-Hardened P/M Al-Mn-Cu-Mg-Zn Alloys at Elevated Temperature

In order to improve the high-temperature strength of an Al-Cu-Mg alloy, Mn was added at supersaturation to form a high-density dispersion of an intermetallic phase. In the P/M Al-3.6Mn- 6.4Cu-3.6Zn-1.7Mg alloy (mass%), rod-like Al-Mn-Cu-Zn quaternary intermetallic phases (Q phase) several hundred nanometers in length were dispersed in the matrix. The chemical composition of the Q phase was determined by TEM/EDX to be 78.8Al-12Mn-8Cu-1.2Zn (at%). The crystal system, space group, and lattice parameters of the unit cell were identified to be orthorhombic, Cmcm and a = 0.76, b = 2.11, c = 1.25 nm, respectively, by Rietveld analysis. Since the matrix of the alloy obtained was of the Al-Cu-Mg-(Zn) system, age-hardening occurred by formation of a GPB zone at room temperature and 448 K. At the peak level of age-hardening at room temperature, the tensile strength at room temperature was 704 MPa, and the elongations were 8.0%. The high temperature strengths at 523 and 573 K were 319 and 141 MPa, respectively, and the elongations were 17 and 34%, respectively.