EFFECT OF ADDITIONAL ALLOYING AND HEAT TREATMENT ON THE PHASE COMPOSITION AND MORPHOLOGY IN Al-Mg-Si TYPE CASTING ALLOY

Authors

  • Viktoriya Boyko National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kiev, Ukraine
  • Edward Czekaj Zakład Stopów Metali Nieżelaznych Instytut Odlewnictwa (IOd), Krakow
  • Małgorzata Warmuzek Laboratorium Badań Struktury i Właściwości Instytut Odlewnictwa (IOd), Krakow
  • Kostiantyn Mykhalenkov National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kiev, Ukraine http://orcid.org/0000-0002-2150-8837

DOI:

https://doi.org/10.7494/mafe.2017.43.3.219

Keywords:

casting alloys, high pressure die casting, aluminium alloys, structure, precipitation, heat treatment

Abstract

The structure of permanent mold and high pressure die castings of the AlMg5Si2Mn alloy after alloying with Li and Sc has been investigated by scanning and transmission electron microscopy, hardness and microhardness measurements, energy dispersive X-ray analysis. Three conditions, as cast, solution treated and aged, were investigated. It was shown that in as-cast state, the structure of an alloy having the nominal composition AlMg5Si2Mn consists of four phases: first – the Al based solid solution, second – the (Al)+(Mg2Si) eutectic, third – the primary Mg2Si crystals and fourth – the a-Al(Mn, Fe)Si phase. Similar phases were observed in the alloys containing Sc or Li. After two days of storing in an as-cast condition, the solid solution in all tested alloys decomposes
and forms zebra-crossing shaped precipitates. TEM examinations revealed that these precipitates nucleate heterogeneously on dislocations. The solution treatment at 575.0°C results in spheroidization of the Mg2Si lamellas, dissolution of the precipitates and formation of a-Al(Mn, Fe)Si dispersoids, nucleating on the surfaces of Mg2Si lamellas. In the Sc containing alloys, the formation of Al3Sc was detected after 120 min soaking. Further heating resulted in the growth of these precipitates. Aging of the Al-Mg-Si alloys leads to an increase of hardness in all studied alloys. This effect is mainly related to precipitation strengthening, via solid solution decomposition and formation of b’’-phase. In Li-alloyed specimens, plates of b Mg2Si phase were observed together with small cubic-shaped d’ Al3Li precipitates.

 

The structure of permanent mould and high pressure die castings of the AlMg5Si2Mn alloy after alloying with Li and Sc has been investigated by scanning and transmission electron microscopy, hardness and microhardness measurements, energy dispersive X-ray analysis. Three conditions, as cast, solution treated and aged, were investigated. It was shown that in as-cast state, the structure of an alloy having the nominal composition AlMg5Si2Mn consists of four phases: first - the Al based solid solution, second - the (Al)+(Mg2Si) eutectic, third - the primary Mg2Si crystals and fourth – the  phase. Similar phases were observed in the alloys containing Sc or Li. After two days of storing in an as-cast condition, the solid solution in all tested alloys decomposes and forms zebra-crossing shaped precipitates. TEM examinations revealed that these precipitates nucleate heterogeneously on dislocations. The solution treatment at 575.0°C results in spheroidization of the eutectic, dissolution of the precipitates and formation of  dispersoids, nucleating on the surfaces of Mg2Si lamellas. In the Sc containing alloys, the formation of Al3Sc was detected after 120 min soaking. Further heating resulted in the growth of these precipitates. Aging of the Al-Mg-Si alloys leads to an increase of hardness in all studied alloys. This effect is mainly related to precipitation strengthening, via solid solution decomposition and formation of b²-phase. In Li-alloyed specimens, plates of b Mg2Si phase were observed together with small cubic-shaped d¢ Al3Li precipitates.

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Author Biographies

Viktoriya Boyko, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kiev, Ukraine

Associated professor, Institute of Fundamentals of Metals Technology, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kiev, Ukraine

Edward Czekaj, Zakład Stopów Metali Nieżelaznych Instytut Odlewnictwa (IOd), Krakow

Dr. hab. inż. Prof.

Małgorzata Warmuzek, Laboratorium Badań Struktury i Właściwości Instytut Odlewnictwa (IOd), Krakow

Dr. hab. inż., Prof.

Kostiantyn Mykhalenkov, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kiev, Ukraine

Professor, director of the Institute of Fundamentals of Metals Technology, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kiev, Ukraine

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Published

2018-06-21

How to Cite

Boyko, V., Czekaj, E., Warmuzek, M., & Mykhalenkov, K. (2018). EFFECT OF ADDITIONAL ALLOYING AND HEAT TREATMENT ON THE PHASE COMPOSITION AND MORPHOLOGY IN Al-Mg-Si TYPE CASTING ALLOY. Metallurgy and Foundry Engineering, 43(3), 219. https://doi.org/10.7494/mafe.2017.43.3.219

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