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Influence of Chemical Composition Variation and Heat Treatment on Microstructure and Mechanical Properties of 6Xxx Alloys

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Influence of Chemical Composition Variation and Heat Treatment on Microstructure and Mechanical Properties of 6Xxx Alloys Volume 46 International Scientific Journal Archives Issue 2 published monthly by the of Materials Science December 2010 World Academy of Materials The aluminum alloys of 6xxx group have been studied After artificial aging, a set of specimens were prepared for extensively because of their technological importance and tensile testing to study the effect of T6 heat treatments on and Engineering Pages 98-107 and Manufacturing Engineering exceptional increase in strength obtained by precipitation mechanical properties of the examined alloys. The specimens hardening. The 6xxx aluminium alloys are mostly used as were strained by tensile deformation on Instron TTF-1115 extruded products, as well as for construction and automotive servohydraulic universal tester at a constant rates at room application. The ease with which these alloys can be shaped, their temperature in according to standard PN-EN 10002-1:2004 [23]. low density, their very good corrosion and surface properties and Tensile properties (tensile and yield strength; elongation) were good weldability are factors that together with a low price these evaluated using round test specimens of 8 mm diameter and 65 Influence of chemical composition variation make them commercially very attractive. mm gauge length (according to ASTM E602-78T [24] standard). The precipitation of metastable precursors of the equilibrium A metallographic investigations were performed on the ȕ(Mg2Si) phase occurs in one or more sequences which are quite samples at as-cast state after homogenization treatment and and heat treatment on microstructure and complex. The precipitation sequence for 6xxx alloys, which is extrusion forging process. The microstructure of the alloys was generally accepted in the literature [11-13], is: observed using optical microscope - Nikon 300 on polished mechanical properties of 6xxx alloys SSSS ĺatomic clusters ĺGP zones ĺE''ĺ E'ĺ E (stable) sections etched in Keller solution containing 0.5 % HF in 50ml Some authors [8] consider the GP zones as GP1 zones while H2O. The surfaces of fracture of the damaged samples were the E'' is called a GP2 zone. The most effective hardening phase prepared to microscopic examination by scanning electron for this types of materials is E''. The medium strength AlMgSi microscopy (SEM). G. Mrówka-Nowotnik* aluminium alloys are commonly processed by extrusion. Their Department of Materials Science, Rzeszow University of Technology, extradubility depends to a large extent on chemical composition, ul. W. Pola 2, 35-959 Rzeszów, Poland casting condition and heat treatment parameters (eg. 3. Results and discussion * Corresponding author: E-mail address: [email protected] homogenization treatment) which determine the microstructure of the billet before extrusion. The microstructure of the 6061 alloy in as-cast state and after Received 10.09.2010; published in revised form 01.12.2010 homogenization is given in Fig. 1 - as an example of as-cast state of the investigated alloys. ABSTRACT 2. Material and experimental a) Purpose: The main task of this work was to study the effect a the precipitation hardening on the microstructure The investigation has been carried out on the commercial and mechanical properties of 6061, 6063 and 6082 aluminium alloys. 6061, 6063 and 6082 aluminum alloys. Chemical composition of Design/methodology/approach: In this paper differential scanning calorimetry (DSC) and hardness the alloys is indicated in Table 1. measurements have been utilized to study the effect of a precipitation hardening on the mechanical properties in 6xxx aluminium alloys. The mechanical (Rm and Rp0.2) and plastic (A, Z) properties of the examined alloys were evaluated Table 1. by uniaxial tensile test at room temperature. The microstructure was observed using optical microscope - Nikon 300, Chemical composition of the investigated alloys, %wt scanning electron microscope HITACHI S-3400 (SEM) in a conventional back-scattered electron mode. Alloy Si Mg Mn Cu Fe Zn Ni Cr Ti Findings: The results show that the microstructure and mechanical properties changes during artificial aging due 6061 0.78 1.07 0.15 0.35 0.16 0.042 0.007 0.35 0.029 a the precipitation strengthening process. Therefore, the parameters (time and aging temperature) of precipitation strengthening process that may lead to the most favourable mechanical properties of 6061, 6063 and 6082 alloys 6063 0.55 0.55 0.07 0.026 0.18 0.02 0.005 - 0.018 were determined. 6082 1.0 0.76 0.56 0.022 0.16 0.013 0.004 - 0.023 Practical implications: This paper is the part of previous author’s investigations which results in modification of the heat treatment parameters that may lead to the most favorable mechanical properties of 6xxx alloys. Originality/value: The paper has provided essential data about influence chemical composition and aging Thermal processing of the investigated alloys included a b) parameters on the microstructure and mechanical properties of 6061, 6063 and 6082 alloys. homogenization treatment and T6 heat treatment (artificially ageing after solution treatment). The temperature of Keywords: Metallic alloys; Microstructure; Mechanical properties; Heat tretmeant homogenization treatment of 6xxx alloys were determined on the Reference to this paper should be given in the following way: basis of literature data and calorimetric investigations. The samples G. Mrówka-Nowotnik, Influence of chemical composition variation and heat treatment on microstructure and in as-cast state were preheated in an induction furnace to mechanical properties of 6xxx alloys, Archives of Materials Science and Engineering 46/2 (2010) 98-107. temperature 575°C held for 72 hours and subsequently cooled to room temperature. Additionally all alloys were heated in a MATERIALS resistance furnace for 12 hours at 565°C and then quenched into a water. Subsequently the specimens were subjected to artificial aging at temperature 175oC up to 98 h. In order to determine an influence 1. Introduction technical 6xxx aluminium alloys contents of Si and Mg are in the of time on the kinetics of ageing the Brinell hardness was measured. 1. Introduction range of 0.5-1.2 wt%, usually with a Si/Mg ratio larger than one. DSC samples of the supersaturated 6061, 6063 and 6082 alloys Besides the intentional additions, transition metals such as Fe and were investigated in SETARAM Setsys thermal analyzer fitted with The 6xxx-group contains magnesium and silicon as major Mn are always present. If Si content in Al alloys exceed the a scanning differential calorimeter module. The heat effects addition elements. These multiphase alloys belong to the group of amount that is necessary to form Mg Si phase, the remaining Si is associated with precipitation of GP zones and intermediate commercial aluminum alloys, in which relative volume, chemical 2 present in other phases, such as Al-Fe-Si and Al-Fe-Si-Mn metastable and stable strengthening phase E(Mg Si) were obtained composition and morphology of structural constituents exert 2 Fig. 1. Microstructure of examined 6061 alloy: a) as-cast state, particles [2,4,6-13]. by subtracting a super purity Al baseline run. o significant influence on their useful properties [1-22]. In the b) after homogenization at 575 C/72h 98 98 © Copyright by International OCSCO World Press. All rights reserved. 2010 The aluminum alloys of 6xxx group have been studied After artificial aging, a set of specimens were prepared for extensively because of their technological importance and tensile testing to study the effect of T6 heat treatments on exceptional increase in strength obtained by precipitation mechanical properties of the examined alloys. The specimens hardening. The 6xxx aluminium alloys are mostly used as were strained by tensile deformation on Instron TTF-1115 extruded products, as well as for construction and automotive servohydraulic universal tester at a constant rates at room application. The ease with which these alloys can be shaped, their temperature in according to standard PN-EN 10002-1:2004 [23]. low density, their very good corrosion and surface properties and Tensile properties (tensile and yield strength; elongation) were good weldability are factors that together with a low price these evaluated using round test specimens of 8 mm diameter and 65 make them commercially very attractive. mm gauge length (according to ASTM E602-78T [24] standard). The precipitation of metastable precursors of the equilibrium A metallographic investigations were performed on the ȕ(Mg2Si) phase occurs in one or more sequences which are quite samples at as-cast state after homogenization treatment and complex. The precipitation sequence for 6xxx alloys, which is extrusion forging process. The microstructure of the alloys was generally accepted in the literature [11-13], is: observed using optical microscope - Nikon 300 on polished SSSS ĺatomic clusters ĺGP zones ĺE''ĺ E'ĺ E (stable) sections etched in Keller solution containing 0.5 % HF in 50ml Some authors [8] consider the GP zones as GP1 zones while H2O. The surfaces of fracture of the damaged samples were the E'' is called a GP2 zone. The most effective hardening phase prepared to microscopic examination by scanning electron for this types of materials is E''. The medium strength AlMgSi microscopy (SEM). aluminium alloys are commonly processed by extrusion. Their extradubility depends to a large extent on chemical composition, casting condition and heat treatment parameters (eg. 3. ResultsResults andand discussion homogenization treatment) which determine the microstructure
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