Influence Of Scandium On Microstructure And Properties Of 6066 Aluminum Alloys

Aluminium alloy is being more and more popular because of its low density, high strength-to-weight ratio and good machining ability, etc. As the resource and energy is becoming tight, aluminium alloy has been widely researched and explored especially in fields of aerospace, military and transportation, etc. Rare earth element Sc has the best alloying effect on aluminium alloy and the property of aluminium could be highly improved when a trace of Sc is added into the alloy. So, the application of Sc in aluminium worth being worked on and research on new type of Al-Sc alloy with fine property has great significance.In this paper, the Al-Sc alloy with different content of Sc was prepared by melting and casting techniques. Specific content of Sc was determined by analysis of the micro-structure and mechanical property of Al-Sc alloys in casting state. Alloy with the best content of Sc and alloy without Sc were both solution treated and aged. The best aging temperature and time was selected by hardness index and the effect of heat treatment on micro-structure and mechanical property of casting alloy was researched. Finally, these two kinds of alloy were both hot-extruded. The feature of secondary phase of ex-extruded and extruded alloys in different heat treatment condition was researched as well as the existing state of Sc and the variation of mechanical property.The result shows that grain size is smallest when 0.2%wt Sc is added into 6066 casting alloy and the primary phase Si is basically eliminated. Strength is improved from 160MPa to 208MPa by 23%. However, gross phase AlFeSi and fishbone-like phase π still exsit and make a bad difference on the mechanical property. The best solution treatment process is 530℃,1h and the best aging process is 175℃,4h. The gross phase AlFeSi and phase π could be eliminated after heat treatment, but the needle-like secondary phase is not in its best state which should be further improved. Meanwhile, heat treatments improve the strength of 6066 alloy with 0.2%wt Sc to 333MPa by 60%, but the ductility of the alloy is still bad. Hot extrusion makes a great difference on micro-structure and property of the alloy is the best after the following T6 heat treatment. Gross net-like and needle-like secondary phase disappear after hot-extrusion and they turn into equiaxed granulous AlFeSi with a size of 1-3μm. Al3Sc with a size of 1μm is found in the alloy with Sc. Both the equiaxed granulous AlFeSi and the Al3Sc dispersively distribute in the matrix and is helpful to the performance of the alloy. The strength of the T6 state alloy after hot-extrusion with Sc is improved to 440MPa, the yield strength is improved to 410MPa by 61% to the hot-extruded state alloy and the ductility stay good which has great significance.