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The Effect of Heat Treatment on Microstructure and Mechanical Properties of the Squeezing Cast Al-Zn-Mg-Cu-Sc-Zr Alloy

Author: TuQiang
Tutor: YangFuBao
School: Beijing Nonferrous Metal Research
Course: Materials Science and Engineering
Keywords: Squeeze Casting Al-Zn-Mg-Cu-Sc-Zr alloy Mechanical properties Microstructure
CLC: TG166
Type: Master's thesis
Year: 2011
Downloads: 116
Quote: 0
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Abstract


This paper was prepared by extrusion casting Al-Zn-Mg-Cu-Sc-Zr alloy billet, the use of Brinell hardness measurement, tensile test at room temperature, conductivity test test test Al-Zn-Mg-Cu-Sc-Zr alloy at different heat treatment the mechanical properties and resistance to stress corrosion, and use the microstructure observation (OM), scanning electron microscopy (SEM), X-ray diffraction phase analysis, transmission electron microscopy (TEM) and other means to study the Different heat treatment and mechanical properties of the test alloy microstructure. Experimental studies show that: 1) Al-Zn-Mg-Cu alloy composite add Sc, Zr element, grain has been refined significantly reduced grain size of about 100μm to about 40μm, spherical alloy crystal grain structure is homogeneous. Squeeze casting the Al-Zn-Mg-Cu-Sc-Zr alloy billets density significantly improved, as compared with gravity casting, die casting 100MPa same solidification under pressure, the alloy density increased by about 5%, the pressure continues to increase the density of the basic unchanged. 2) Al-7.8Zn-2.2Mg-l.6Cu-0.2Sc-0.2Zr alloy single-stage solution more appropriate system for the \/ 24h 480 ℃ / 10h water quenching \reach 597MPa and 12.5%. 3) a hardened alloy after solution treatment, the alloy coarse eutectic phase dissolved more fully after quenching the solid solution to increase the degree of supersaturation and the eutectic phase reduced tendency to cause stress concentration, the subsequent strength after aging treatment, plasticity have been significantly improved. 4) Test alloy after 120 ℃ / 24h single-stage aging treatment best mechanical properties, this time co-precipitates mainly within Jinzhong Jing needle η 'and a small amount of short rod η, during aging alloy exhibits a high resistance to aging resistance, strength, hardness, maintain a high stability. After a two-stage aging and RRA treatment significantly decreased the mechanical properties is due to deformation of the cast structure has not been processed, the lack of matrix dislocations, vacancies and other defects makes the GP zones and η 'phase in the second stage aging process can not be timely insulation back to the base solution, the coarsening of precipitates further strength and ductility of the alloy decreases. 5) squeeze casting alloys by the multi-stage solution T6 aging treatment has good resistance to stress corrosion cracking (conductivity 35.6% IACS) and good ductility (elongation 12.5%), the alloy is better resistance to stress corrosion The main reason is the grain boundary precipitates showed a discontinuous distribution, alloy anode in the corrosion process, is an isolated particle, the relative corrosion process slows down; aging the alloy grain boundaries precipitate free zone is 20nm-30nm, width wider, Since no precipitate with softer alloys force during the precipitate at the grain boundaries with no stress at relaxation, alloy plastic is better.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Heat treatment > The heat treatment of non-ferrous metals and their alloys
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