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Grain Refinement of the Al-Cu-Mg-Ag Alloy with Er and Sc Additions

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Grain Re?nement of the Al-Cu-Mg-Ag Alloy with Er

and Sc Additions

YUNTAO LI,ZHIYI LIU,QINGKUN XIA,and YANBIN LIU

The present work investigated the e?ects of additions with Sc and Er on the grain re?nement in

an Al-Cu-Mg-Ag alloy containing minor zirconium.The results indicated that0.32pct Sc

addition interacted with0.11pct Zr and formed primary Al3(Sc,Zr)phase.It acted as the nuclei

for heterogeneous nucleation of a-Al grain growth in the melt and re?ned the grains greatly.

Additions of0.3pct Er resulted in an Al8Cu4Er phase formed at the grain boundary and re?ned

mainly the dendritic substructure.There is no visible interaction of Er and Zr.

DOI:10.1007/s11661-007-9269-4

?The Minerals,Metals&Materials Society and ASM International2007

I.INTRODUCTION

G RAIN re?nement is an important technique to improve the cast quality of the aluminum alloys.It reduces the size of primary a-Al grains in the casting. The re?ned grain restrained coarse columnar grain structure.A?ne equiaxed grain structure leads to several bene?ts,such as high yield strength,high toughness,improved machinability,and excellent deep drawability of the products.[1]There are many methods to re?ne grain,whereas the microalloying or trace elements added to aluminum alloys is the most eco-nomical one.The common grain re?ners of casting aluminum alloys include Al-Ti,Al-B,Al-Ti-C,and Al-Ti-B master alloys.[2–6]An e?ective method to re?ne the grain of heat-treatable alloys was micro-alloying with transition metals or rare earth metals,such as additions of Sc,Zr,and Er as alloying elements.[7–10]

Research on the addition with scandium element in aluminum alloys has been carried out for many years. As an e?cient grain re?ner of casting alloys,Sc forms a Al3Sc phase in aluminum alloys.The Al3Sc phase is a thermostable L12-type(Cu3Au)one,which is charac-terized by a structural and dimensional matching with the aluminum matrix.[11,12]It acts as a nucleation site e?ciently for heterogeneous nucleation of a-Al grain growth in the melt.

When Sc was added to Al-Cu serial alloys,a ternary W phase formed.According to the Al-Cu-Sc ternary phase diagram,[13,14]Al3Sc and a ternary W phase are predominant phases.[15–17]When W primary particles formed in the melt,they made it respond poorly to grain re?nement.[16]However,Yu[18]has found that addition of scandium and zirconium to2618alloy resulted in a primary Al3(Sc,Zr)phase,which re?ned grain signi?-cantly.The Sc added to2024alloy has also been discovered to improve the cast microstructure.[19] Recently,several publications have been concerned with the addition of rare earth Er to aluminum alloys.[16,20,21]The Er addition formed a thermostable L12-type(Cu3Au)Al3Er phase similar to alloying element Sc.It re?ned grain signi?cantly.Zhao[22]studied the Al-Zn-Mg-Cu alloy with addition of Er and found that Er in this alloy mainly forms Al3Er phase.The dispersed Al3Er phase acts as the site for heterogeneous nucleation of g(MgZn2)phase and enhances the mechanical properties.Fu and Yang[23–25]have studied the high pure aluminum and the Al-Mg alloy with addition of Er and found the existence of Al3Er phase. The study carried out by Nie revealed that the addition of Er in Al-4Cu alloy mainly forms a Al8Cu4Er phase.[26]

Al-Cu-Mg-Ag-(Zr)alloys are the promising candi-dates for future use for high-speed aircraft.[27–30]The research carried out by Sadayappan[31,32]indicates that additions with mischmetal in Al-Cu-Mg-Ag series alloys play an important role in reducing the hot tearing propensities.It o?ers a new possibility to re?ne the casting grain with additions of Er and Sc in this class of alloys.

In the present study,three alloys,namely,Al-Cu-Mg-Ag-Zr alloys without addition and added separately with Sc and Er,were prepared.The grain re?ning e?ect with and without additions was studied.The alloying behaviors of Sc and Er were studied in order to con?rm the element interactions during the solidifying process. The mechanism of grain re?nement was discussed.

II.EXPERIMENTAL

Three alloys have been prepared in this article.The normal compositions(mass pct)of the cast alloys are provided in Table I.The base alloy,named alloy1,was prepared using commercial purity Al(99.998pct),Mg, Ag,and Al-50.4pct Cu-Al-4.2Zr master alloys.Other two alloys with Sc and Er additions individually were prepared.The additions were made each to the melt

YUNTAO LI,QINGKUN XIA,and YANBIN LIU,Doctoral

Candidates,and ZHIYI LIU,Professor,are with the College of

Materials Science and Engineering,Central South University,Chang-

sha,Hunan410083,People?s Republic of China.Contact e-mail:

liuzhiyi@/doc/a97014136c175f0e7cd137fa.html

Manuscript submitted January5,2007.

Article published online October5,2007.

METALLURGICAL AND MATERIALS TRANSACTIONS A VOLUME38A,NOVEMBER2007—2853

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