Research On Micro Structure,Performance And Semi-Solid Forming Technology Of Al-Fe Based Alloys

The type, size and distribution of AlFe secondary phases in Al-Fe alloys have an effect on the ultimate properties of the alloys directly. Thekey to extend the applications of Al-5Fe based alloys is to control and improve size and feature of theiron-rich phases and strengthen the Al matrix. The researches in this paper focus on the interaction of alloying elements, Cu, Cr, Mn, Zr, Mg and Zn, in Al-5Fe based alloys, and effects of the elements on formation of AlFe phases, and confirm alloying element behavior of microstructure evolution and effect in preparation processing. The effect of semi-solid forming technology on organization and performance of Al-5Fe based alloys is researched by the semi-solid extrusion simulation. The invigorating effect of AlFe phases on elevating temperature creep of Al-5Fe based alloys is analyzed by tensile creep test. It is helpful for practical Al-5Fe based alloys to provide some experiments and theoretical base.The results show that Al-5Fe based alloys, accounting for about3/4of the total amount of Cu dissolves in the Al matrix and the rest of Cu dissolves into AlFe phase or forming other Cu-containing phases, Cr dissolves only in AlFe intermetallics rather than in the matrix, Mn dissolves mainly in AlFe phases.Cu.Cr, Mndissolved intoAlFephasesmakesthe morphology of AlFephase in Al-5Fe based alloys evolves fromaciculartolamellar,blocky, multi-angular orringshape. Zr, Mg, Zn don't dissolve in AlFe intermetallics, and hinder the growth of Fe-bearingphases indirectly. Cu, Cr and Mn dissolved in AlFe phase can impel metastableAlFe phase formation. They are a favorable nucleant for forming metastableAlFeintermetallicsin Al-5Fe based alloys.In Al-5Fe based alloys,Al2Cu phase is formed at about500℃. Al7Cu2Fe phase can nucleate on Al13Fe4phase, which is froma peritectic reaction:L+Al13Fe4(?)Al7Cu2Fe formation.In a majority of cases, Al7Cu2Fe phase attaches oneself to Al13Fe4phase edges or enveloped the Al13Fe4particles to form a "core-shell" microstructure. Individual a few sheet particles composed of the Al7Cu2Fe phase are also seen in the matrix.The α-Al matrix and thesecondary phases in Al-5Fe based alloys are paramagnetic phases, electromagnetic stirring can reduce the nucleation of critical radius and critical nucleation energy, so a-Al and the second phase particlesare refined.In semi-solid heating re-melting process, low melting Al2Cu Al7Cu2Fephasesare first melted at the grain boundaries and AlFe phase boundary, with the increase of heating temperature and holding time, Cu in the alloy will diffuse from intra-grain tointer-grain or AlFe phases surrounding and gather in the liquid phase, A ratio of Cu content in intra-grain and inter-grain reaches about1:1.6.On semi-solid deformation, the liquid phase in Al-5Fe based alloys plays a powerful regulating role. Cu and Fe elements would enrich in liquid phase and vary with liquid phase change. Al7Cu2Fe and Al2Cu phasesare formed from Cu and Fein the semi-solid extrusion processing, and their distribution is consistent with the distribution of the liquid phase in the alloy. The deformation increases to a certain extent, semi-solid squeeze hasan amplification effect on the stress of isolation of closed liquid region, resulted in crushing AlFe phase to create mechanical condition.High strain rate can reduce the segregation of the liquid phase.High liquid fraction can reduce the peak true stress.The high liquidfraction and high strain rate would be a good forming process.The creepof Al-5Fe based alloys has larger sensitive to creep temperature and stress.In deformation processing, the dislocations general climb over the dispersion particles, an attractive interaction between dislocations and dispersion particles is weak.The AlFe secondary phases in Al-5Fe based alloys are valid provided with bearing loads and transferring loads and reduces effective stress for creep of the matrix, result in the creep rate of the alloy decreases and improves the creep resistance of the material.Al-5Fe based alloys strengthening mechanism is effective load transfer of AlFe secondary phases.Semi-solid forming has obvious re-dissolution effect,so that the tensile strength of Al-5Fe based alloys prepared by the semi-solid formation is greater than270MPa, the elongation is greater than1%.The supersaturated solid solution precipitates during subsequent low temperature aging, result in as-aged tensile strength of the alloy higher than as-extruded that16%, elongation higher than27%, taking full advantage of the potential of the alloy age hardening.Al-5Fe based alloys with high temperature performance and good heat resistance can meet the engineering applications in the temperature of the working environment in about250℃.