Micro-alloying and Mechanism of Al-Zn-Mg-Cu Ultra High Strength Aluminum Alloy Prepared by Rapid Solidification
|School||Harbin Institute of Technology|
|Course||Materials Processing Engineering|
|Keywords||ultra high strength Al alloy composition calculation deposition trace element microstructure|
The billet of Al-Zn-Mg-Cu super-alloy was prepared by the spray forming processing and then was consolidated by extrusion. Phase structure, solid solubility and the effects of trace alloying elements, precipitated phase, performance prediction were investigated by means of X-ray(XRD), scanning electron microscope(SEM) and transmission electron microscope(TEM). The results showed that the solid solubility of as-deposited alloy was higher than that of casting alloy by theoretic calculation. The solid solubility of alloy1(Al-12Zn-3.34Mg-1.12Cu-0.2Zr-0.2Mn-0.16Cr) and alloy2(Al-10Zn-3.49Mg-1. 25Cu-0.25Zr-0.2Mn-0.16Cr) were 5.7% and 6.2% by X-ray, respectively. The grain size is about 20～30μm in as-deposited alloy. There is little effect on grain size with the Zn content increasing, while in the grain boundary with a little increase in thickness. Ternary compound(Al, Zn, Mg) distributed within grains and grain boundary. The Cr and Mn exists as a long strip shape compound, Al12(Cr, Mn), in as-deposited alloy and not react with element of Zn and Mg. The quantity of precipitated phase was not effected during aging treatment. Based on the assumption that strength of alloy is made of linear superposition of matrix strength, grain refinement strengthening, solid solution strengthening and precipitation strengthening, the predicted strengths of alloy1 and alloy2 were 662.5±72.5MPa and 712±25MPa. Solid solution strengthening was the greatest contribution to matrix strength. The spray deposited alloy gets to the peak age condition while aged at 120℃for 16 hours and the most precipitated phase. The size of the dispersive phase is about 45nm. The precipitated uniformly Al3Zr particles have coherent relation with the matrix and block movement of dislocation and pin dislocation.