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TESTING 1-2-3


Boosting Aluminum-Silicon’s Strength, Ductility in a Permanent Mold Casting


Researchers are investigating additional lightweight alloys in permanent mold castings. MOHAMMAD SHAMSUZZOHA & LAURENTIU NASTC, UNIV. OF ALABAMA, TUSCALOOSA, ALABAMA; DAVID WEISS, ECK INDUSTRIES, MANITOWOC, WISCONSIN; AND JOHN T. BERRY, MISSISSIPPI STATE UNIV., STARKVILLE, MISSISSIPPI


so-called green practices. T e North American metalcasting industry faces increased government regulation for better fuel effi ciency and lower emis- sions in the aerospace, automotive and defense industries. T e challenge is to produce components that minimize weight without sacrifi cing mechanical or physical properties. Hypoeutectic aluminum-silicon


T 1


2 3


alloys have a silicon content less than eutectic compositions, mean-


ADDING IT ALL UP Breaking down the latest research is as easy as 1-2-3.


“Permanent Mold Castings of High-Strength and High Ductility Ba-Treated Hypo-Eutectic Al-Si Alloys,” Mohammad Shamsuzzoha and Laurentiu Nastc, Univ. of Alabama, Tuscaloosa, Ala.; David Weiss, Eck Industries, Manitowoc, Wis.; and John T. Berry, Mississippi State Univ., Starkville, Miss.


Background—Hypoeutectic Al-Si alloys are used in high strength applications that also require good ductility. This group of alloys may improve already desirable characteristics when treated with small amounts of barium. Such alloys, contain- ing interdendritic eutectic microstructure, may offer engineers strength and ductility not currently seen in existing cast alloys. These alloys may be further strengthened by heat treatment.


Procedure—Al-Si alloys with 6-10% silicon were melted, cast into a permanent mold and then heat treated. The samples then were subjected to tensile testing. The microstructure of the alloys was studied using scanning electron microscopy. Samples were etched to remove surface aluminum and expose the topography and morphology of the silicon phase.


Results and Conclusions—The microstructure of the hypoeutectic Al-Si-Ba alloys cast in a permanent mold exhibit high UTS and ductility values. The solid Ba solution in silicon appears to affect the crystallization of both the primary Al and eutectic silicon in the hypoeutectic Al-Si-Ba alloys when cast in a permanent mold. The effect allows the hypoeutectic melt to nucleate eutectic silicon and primary aluminum crystal, resulting in the development of high-strength, highly duc- tile Al-Si alloys.


44 | MODERN CASTING March 2016


he entire supply chain—metal casting suppliers and purchasers included—are conscious of minimizing waste and cost, while improving


ing the silicon content is usually between 5-12%. These alloys are used in high strength applications that also require good ductility. This group of alloys, when treated with small amounts of barium, may further improve already desirable mechanical properties: light weight and high strength. Such alloys, containing interdendritic eutectic microstructure, may offer engineers strength and ductility not currently seen in existing cast alloys. These alloys also may be further strength- ened by heat treatment. In the research paper, “Permanent Mold Castings of High-Strength and High Ductility Ba-Treated Hypoeu-


tectic Al-Si Alloys,” a research team investigated how barium treatments aff ected aluminum-silicon alloys in an eff ort to develop advanced alloys that could be cast.


Question


Can the addition of barium to aluminum-silicon cast alloys increase ductility and strength in as-cast and/or T6 heat-treated conditions?


1


Background Based upon the Al-Si


binary system shown in Figure 1, alloys with hypo- eutectic composition have a


silicon composition below 12.7 wt%.


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