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

Abstract

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 multiple additives (Mn and Zr) on microstructure of P/M 7000 series aluminum alloys

“…The microstructure is composed of fine grains having a diameter of 1ìm and fibrous grains elongated along the extrusion direction (ED). It is reported that atomized powders have mainly some coarse grains with a diameter of above 10ìm and have few fine grains with a diameters of 5 μm [3]. So, the fine grains observed in the extruded alloys (or Fig.3) are considered to be formed by DRX during hot extrusion.…”

Microstructures and precipitation behaviour of cryomilled Al–Zn–Mg–Cu–Mn powders

“…Osamura had believed that manganese dispersoids were Al 11 Mn 3 (ZnCu 2 ) in their early work, 7 but their recent results showed that the Mn containing precipitates were granular Al 6 Mn and rodlike Q phase with a composition of Al-10?3Mn-4?2Cu-2?5Zn-2?5Mg (wt-%). 9 Lim 8 and Park 6 supposed that the Mn rich phase was Al 24 Mn 5 Zn. Marants 11 had reported that Mn rich phase had a structure of Al 20 Cu 2 Mn 3 based on X-ray analysis, but the weight ratio of copper and manganese in the dispersoids was about 1 : 2 according to the electron probe microanalysis.…”

“…[1][2][3] Alloying with Mn has been shown to be an effective way to increase the strength of Al-Zn-Mg-Cu series alloys. [4][5][6][7][8][9][10] It is generally accepted that the main reason for the increase in the tensile strength is the precipitation of insoluble fine Mn bearing dispersoids from supersaturated a-Al matrix. The Mn bearing dispersoids could promote the homogeneous slip, refine the slip bands and decrease the local strain or stress concentration.…”

“…Most of the previous investigations on Al alloys with manganese addition have been focused on strengthening effect of Mn element to Al alloys. However, Few detailed studies on the decomposition of supersaturated 7000 series Al alloy has been carried out, 9,11 especially with high alloying elements content (total content of alloying elements >12%). The aim of the present work was to provide an understanding of microstructural evolution and phase transformation in supersaturated Al-Zn-Mg-Cu-Mn alloy powders during subsequent processing.…”