【作者】 刘波；

【导师】 袁晓光；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2012， 博士

【摘要】 Al-Fe合金中AlFe第二相的形貌、尺寸和分布直接决定着合金的最终性能。因此,细化及改善AlFe相尺寸和相貌,强化合金基体成为Al-5Fe基合金实用化的关键。本研究通过采用Cu、Cr、Mn、Zr、Mg、Zn等元素合金化,探索合金元素在Al-5Fe基合金中的相互作用及对第二相形成的影响,确定合金化元素在组织演化及制备工艺过程中的行为；通过半固态挤压热模拟,研究半固态成形工艺对Al-5Fe基合金组织和性能；通过高温拉伸蠕变实验,分析AlFe第二相对合金高温蠕变的强化作用,为Al-5Fe基合金的实用化提供了实验和理论基础。研究结果表明：在Al-5Fe基合金中,约3/4的Cu溶入基体,其余的Cu溶于AlFe相或形成其它的含Cu相；Cr只溶解于AlFe相中,而不溶于基体；Mn主要溶解在AlFe相中。溶入AlFe相中的Cu、Cr、Mn可使针状的AlFe相转变成片状、块状、多角状或环形状。Zr、Mg、Zn不溶于AlFe相中,只能间接的阻碍AlFe相的生长。溶于AlFe相中的Cu、Cr、Mn可促进AlFe亚稳相的形成,它们是亚稳的AlFe相的很好形核剂。Al2Cu相是在500℃左右形成。Al7Cu2Fe相可在Al13Fe4相上形核,大部分由包晶反应：L+Al13Fe4(?)Al7Cu2Fe形成,故大部分的Al7Cu2Fe相会依附在Al13Fe4相的边缘或四周,形成“核-壳”结构。但在基体中也发现少量的独立的片状的Al7Cu2Fe相。Al-5Fe基合金中的α-Al基体和第二相是顺磁性相,电磁搅拌可以降低其形核的临界半径和临界形核功,使α-Al和第二相颗粒细化。在半固态加热重熔过程中,低熔点的A12Cu、Al7Cu2Fe等相首先在晶界和AlFe相边界溶化,随着加热温度的升高和保温时间的增加,合金中的Cu元素从晶粒内向晶界或AlFe相周围扩散,在液相中富集,使晶内的和晶界的Cu量到达约1：1.6。液相在半固态变形中起着强大的调节作用。Al-5Fe基合金在半固态变形时,液相中会富集Cu、Fe元素,并伴随着液相的变化而变化,Cu、Fe在半固态挤压时形成Al7Cu2Fe、Al2Cu等相,其分布与液相的分布一致。当变形增大到一定程度,半固态挤压对孤立封闭的液相区域的应力具有放大效应,为挤压破碎AlFe相创造力学条件。高应变速率变形可减轻液相的偏析,高液相分数可降低真应力峰值,故高液相、高应变速率是一种较好的成型工艺。Al-5Fe基合金对蠕变温度和蠕变应力有较大的敏感性。变形过程中,位错按整体攀移的方式越过弥散粒子,位错与弥散粒子之间的相互作用较弱。合金中的AlFe第二相具有有效的承载与传载作用,减小了使基体发生蠕变的有效应力,使合金的蠕变速率下降,提高了材料的抗蠕变能力。AlFe第二相的有效传载是Al-5Fe基合金的强化机制。半固态成型具有明显的回溶效应,使半固态成型制备的Al-5Fe基合金挤压态的室温抗拉强度大于270MPa,伸长率大于1%；经后续的低温时效,使合金时效态的抗拉强度高于挤压态的16%,伸长率高于27%,充分利用了合金时效硬化的潜力。Al-5Fe基合金具有很高的高温性能和良好的耐热性,可满足在250℃左右温度工作环境下的工程应用。更多还原

【Abstract】 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℃.更多还原