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Age-hardening Behavior and Microsturetural Characterization of Precipitates in Al-Mg-Si-Cu: 6005A Alloy

Author: YangWenChao
Tutor: WangMingPu
School: Central South University
Course: Materials Physics and Chemistry
Keywords: 6005A alloy Precipitation hardening Aging sequence The HRTEM SADP analysis Transformation matrix Strengthening effect
CLC: TG156.92
Type: PhD thesis
Year: 2011
Downloads: 340
Quote: 1
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Abstract

As can be heat-strengthened aluminum alloy, Al-Mg-Si-Cu alloy having a medium strength, good corrosion resistance, excellent moldability, as well as lower density, and is currently has occupied most of the world's aluminum market and proportion. Good macroeconomic performance can not be separated from the alloy microstructure, and the microstructure and some nano-precipitated phase crystal structure and phase transition process closely linked. Regulate the organization of Al-Mg-Si-Cu alloy, as well as some of the nano-precipitated phase structure, size, shape and distribution of nano and atomic scale is a fundamental way and effective way to achieve its performance optimization. This paper selected Al-Mg-Si-Cu system the 6005A alloy extrusion as the research object, using a conventional transmission electron microscope (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SADP) techniques, 6005A alloy extrusion online quenched microstructure and texture in the alloy during aging hardening behavior and phase transformation, nano-aging precipitation the phase microscopic structure and of precipitated phase structure on the macroscopic properties of the alloy system, the purpose of deepen understanding of 6005A alloy properties and process from the atomic and nano-scale, the theoretical basis for exploring the alloy modified with new technology and new ideas. This study obtained the following conclusions: (1) 6005A alloy extrusion grain fiber distribution, average size of 50 microns or about, the the crystalline memory in a lot of Mg2Si phase, containing a small amount of the Fe AlFeMnMgSi phase and containing Mn, Cr and the AlCrMnMgSi phase; by solution heat treatment of 550 ° C / 1 h, most of the Mg2Si phase back to the melting, the Fe-containing Mn, Cr phase can not be eliminated; brass {110} lt; 112 GT; texture and recrystallization cubic type {001} lt; 001 GT; texture, by solution and aging treatment, the texture did not change significantly. (2) 6005A alloy processed by a single-stage aging, 175 ° C / 12h reaches a hardness peak hardness of 120HV beta phase exists for a long time, after the peak, which in the matrix, the alloy exhibits significant anti-aging ability to soften, 90h, hardness began to rapidly decline; 200 ° C aging, 4h to reach the peak hardness hardness 113Hv, after the peak, the beta phase is rapidly disappearing, alloy apparent over-aging to soften. Variable-temperature aging treatment, a hardness peak in the vicinity of 100 ° C and 250 ° C, respectively, corresponding to several clusters and GP zones and beta \small clusters occur back to dissolve the alloy hardness decreased. By the second aging treatment, alloy 18h can reach peak hardness, hardness 127Hv, which interrupt the aging treatment can produce more small, dispersed GP zone, more fully for the beta phase precipitation nucleation. (3) with the vacancy binding energy and the equilibrium phase diagram analysis, we found that in the early age-hardening process, the Si atoms in the Al-Mg-Si-Cu alloy control co-Mg-Si clusters and the number of GP zones, and alloys age-hardening process plays a dominant role. combined with TEM Organization observed the 6005A alloy aging sequence can be expressed as: SSSS → Si-vacancies on the Mg-vacancy clusters and the dissolution of Mg-rich clusters → Mg-rich clusters and rich Si atoms → free Mg atoms diffuse to the Si-rich clusters → Mg-Si co-clusters → GP District → Asia stable beta phase → metastable beta 'and Q' → stable p-phase and Q-phase. (4) HRTEM study showed that the beta phase having a C-heart monoclinic structure, the lattice parameters: a = 1.516m, b = 0.405nm, c = 0.674nm, beta = 105.26 °; P 'phase and Q' phase are HCP structure, wherein beta 'phase lattice parameters: a = 0.715nm, c = 0.405nm, gamma = 120 °, Q' relative to the lattice parameters: a = 1.032nm, b = 0.405nm , gamma = 120 ° (5) the 6005A alloy in three main precipitated phase (beta, p 'and Q' phase) has 12 variants, and the Al matrix orientation relationship can be respectively expressed as: (010 ) beta / / {100} Al, [001] beta / / lt; 310 GT; Al and [100] beta / / lt; 230 GT; Al; (0001) beta '/ / {100} Al [2110] beta '/ / lt; 310 GT; Al and [1210] beta' / / lt; 110 GT; A1; (0001) Q '/ / {100} Al, [2110] Q' / / lt; 510 the GT; Al, and [1210] Q / / lt; 110 GT; Al (6) proposed a set of HRTEM structural characterization, matrix calculation, the diffraction pattern simulation and pole figure analysis as one of the use of this method can be very scientific analysis of any one of any alloy precipitate orientation relationship between the phase and matrix as well as any zone axis SADP phenomenon whereby 6005A Jinfeng aging and over-aging state [001] Al zone axis SADP model of the aging process of the emergence of some of the \[304] beta and [106] beta with shaft under the ± 1-order diffraction spots; the overaged state \and [3210] Q band axis of the diffraction spots. (7) TEM and SADP studies show that, along the A1 base body [001] Al direction precipitated beta \with axes, namely: [010] beta \Q 'and [3210] Q' According to the North, were lying down and insert different orientations of the beta phase, beta 'phase and Q' phase of the detail HRTEM structural characterization of beta 'phase and Q' phase the moire stripes made;, but also found that the presence of some internal dislocation will make the number of interface dislocations precipitated phase deviation from the theoretical value. Showed that (8) HRTEM studies and beta \surface of cells; Q 'phase and A1 substrate (200) Al basically coherent, semi-coherent (020) Al surface. eligibility differences caused by differences in three main precipitation strengthening effect from the strain the field viewpoint strengthening sequence can be expressed as: beta phase gt; Q 'phase gt; p' phase. (9) According to the interface control growth theory beta \coherent and fundamental lattice along its minor axis with matrix non-coherent and easy to grow in a plate shape, its cross-sectional morphology; beta 'phase is more incoherent than Q' phase more coarse.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Heat treatment > Heat treatment process > Special heat treatment > Aging treatment
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