Investigation of the Effects of Ni, Fe, and Mn on the Formation of Complex Intermetallic Compounds in Al-Si-Cu-Mg-Ni All
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I.
INTRODUCTION
MULTICOMPONENT Al-Si alloys are wildly used as piston materials and demands have been increased on the performance of these alloys.[1,2] Meanwhile, the addition of transition metals has received considerable attention to improve the properties of aluminum piston alloys, especially at elevated temperatures. Iron and manganese can be beneficial for improving the thermal stability of the alloy, as well as nickel, which is a vital element in piston alloys.[3–8] Different types of piston alloys usually contain 11 to 23 wt pct Si, 0.5 to 5.5 wt pct Cu, 0.6 to 1.3 wt pct Mg, 0.5 to 3 wt pct Ni, up to 1.3 wt pct Fe, and up to 1 wt pct Mn. Belov et al. did remarkable work on the phase diagram of the Al-Si-Cu-Mg-Ni alloying system, with and without considering the influence of Fe. Figure 1(a) shows the distribution of phases in the solid state of the Al-Si-Cu-Mg-Ni system. The possible phases in equilibrium with (Al) and (Si) are composed of Al3Ni, Mg2Si, Al2Cu, Al3CuNi, Al7Cu4Ni, and Al5Cu2Mg8Si6. Also, Figure 1(b) demonstrates the polythermal projection of solidification surfaces in this alloying system. Taking Fe into account, Al9FeNi, Al5FeSi, Al8FeMg3Si6, and Al15(Fe,Mn)3Si2 (in the presence of Mn) are added to the phases of the Al-Si-Cu-Mg-Ni system.[9,10] Iron is usually considered as an impurity in Al-Si alloys; however, this element, as an alloying element, has some benefits such as maintaining the strength of alloys R. GHOLIZADEH, M.Sc. Student, and S.G. SHABESTARI, Professor, are with the Center of Excellence for Advanced Materials Processing (CEAMP), School of Metallurgy and Materials Engineering, Iran University of Science and Technology (IUST), 16846 Narmak, Tehran, Iran. Contact e-mail: [email protected] Manuscript submitted December 4, 2010. Article published online June 23, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
at high temperature due to the formation of heatresistant intermetallic compounds.[3] The platelet Al5FeSi phase is the most harmful Fe-containing phase in Al-Si cast alloys. This needlelike phase was reported to enhance crack initiation and decrease the ductility of the castings.[11,12] In recent years, many experimental studies have attempted to modify the morphology of the Al5FeSi phase into a less harmful form through the addition of alloying elements such as Mn,[13] Ni,[14] Sr,[15,16] Mg,[17,18] and Be.[18,19] Among these modifying elements, Mn was reported generally to decrease the detrimental effect of Fe and forms Al15(Fe,Mn)3Si2 or Al12(Fe,Mn)3Si2 phase. This quaternary phase forms different shapes such as chinese script, polyhedral, or starlike morphologies. As a rule of thumb, the optimum amount of Mn usually added to the alloys is equal to half of the Fe content.[11,13,20–26] The aim of this work is to study the formation of intermetallic compounds by substituting Fe and Mn for Ni in high Ni-containing 3HA alloy. The formation of intermetallic phases will be studied through computeraided thermal analysis and microstructural observation.
II.
EXPERIMENTAL PROCEDURE
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