Effects of Zn/Cu Ratio and Silicon on Microstructure, Mechanical Properties, Tarnish and Corrosion Resistance of As-Cast 940 Silver Alloys

Jirutthitikalpongsri Hirunyagird; Amnuaysak Chianpairot; Ekasit Nisaratanaporn; Gobboon Lothongkum

doi:10.3139/120.110614

Article

Effects of Zn/Cu Ratio and Silicon on Microstructure, Mechanical Properties, Tarnish and Corrosion Resistance of As-Cast 940 Silver Alloys

Jirutthitikalpongsri Hirunyagird , Amnuaysak Chianpairot , Ekasit Nisaratanaporn and Gobboon Lothongkum

Published/Copyright: September 28, 2014

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From the journal Materials Testing Volume 56 Issue 9

Abstract

This work studies the effects of Zn/Cu ratio and silicon on the improvement of mechanical properties, tarnish and corrosion resistance of 940 silver alloys. The silver alloys to be investigated are divided into 2 groups. The group 1 alloys are Ag-Cu-Zn alloys. The group 2 alloys are Ag-Cu-Zn-0.02Si alloys. The microstructures of all alloys to be tested look similar and consist of a Ag-rich matrix (α phase) and Cu-rich eutectic structure (α + β phase). The proportion of eutectic structure decreases by increasing Zn/Cu ratio. Increasing Zn/Cu ratio significantly decreases hardness, ultimate tensile strength, but markedly increases elongation. Addition of 0.02wt.- %Si to Ag-Cu-Zn alloys has no effect on hardness and ultimate tensile strength, but decreases elongation. The tarnish and corrosion resistance of Ag-Cu-Zn alloys in 1 % NaCl solution at 298 K significantly increases with increasing Zn/Cu ratio. Addition of silicon also improves tarnish resistance.

Kurzfassung

In den diesem Beitrag zugrunde liegenden Arbeiten wurden die Auswirkungen des Zn/Cu-Verhältnisses sowie von Silizium auf die Verbesserung der mechanischen Eigenschaften, Anlauffarben und Korrosionsresistenz von Silber 940 Legierungen untersucht. Die zu untersuchende Silberlegierungen wurden in zwei Gruppen eingeteilt. Die Legierungen der Gruppe 1 sind Ag-Cu-Zn Legierungen. Die Legierungen der Gruppe 2 sind Ag-Cu-Zn-0.02Si Legierungen. Die Mikrostrukturen aller zu untersuchende Legierungen sehen vergleichbar aus und bestehen aus einer Ag-reichen Matrix (α Phase) und einer Cu-reichen eutektischen Strutur (α + β Phase). Der Anteil der eutektischen Struktur nimmt mit zunehmendem Zn/Cu-Verhältnis ab. Ein zunehmendes Zn/Cu-Verhältnis vermindert die Härte und Zugfestigkeit signifikant, erhöht aber markant die Dehnbarkeit. Die Zugabe von 0.02 Gew.- % Si zu den Ag-Cu-Zn Legierungen hat keinen Effekt auf die Härte und die Zugfestigkeit, vermindert aber die Dehnbarkeit. Die Resistenz gegen Anlauffarben und Korrosionserscheinungen der Ag-Cu-Zn Legierungen in einer 1 % NaCl-Lösung bei 298 K steigt signifikant mit zunehmendem Zn/Cu Verhältnis an. Außerdem verbessert die Zugabe von Silizium die Resistenz gegen Anlauffarben.

*Correspondence Address Gobboon Lothongkum, Assoc. Prof. Dr.-Ing Innovative Metals Research Unit, Department of Metallurgical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand

Jirutthitikalpongsri Hirunyagird, born in 1981, is PhD student at the Department of Metallurgical Engineering, Faculty of Engineering, Chulalongkorn University, Thailand. She received a bachelor degree in metallurgical engineering from Suranaree University of Technology, Thailand in 2000. Her research scope is related to development of jewelry alloy.

Amnuaysak Chianpairot, PhD, is researcher at Failure Analysis and Materials Corrosion Lab, Materials Reliability Research Unit, National Metal and Materials Technology Center. He received his master degree in metallurgical engineering from University of California, Berkeley, USA and received his PhD in metallurgical engineering from Chulalongkorn University, Thailand. His research interest is corrosion and failure analysis.

Ekasit Nisaratanaporn, PhD, is currently director of Metallurgy and Materials Science Research Institute (MMRI), Chulalongkorn University, Thailand. He is also holding a professor position and associates with Innovative Metals Research Unit at the Metallurgical Engineering Department, Chulalongkorn University, Thailand. His work is primarily based on jewelry metals. He also holds a head position of the Innovative Metals Research Unit at Chulalongkorn University.

Gobboon Lothongkum, the corresponding author, is associate professor and member of the Innovative Metals Research Unit, Department of Metallurgical Engineering, Faculty of Engineering, Chulalongkorn University, Thailand. He received his Dr.-Ing. degree from the Helmut-Schmidt-University, University of the Federal Armed Force Hamburg, Germany in 1994 and the International Welding Engineer Certificate of the International Institute of Welding in 2006. His areas of expertise include corrosion of metals and alloys, welding and metal joining, stainless steels, and high temperature materials.

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Published Online: 2014-09-28

Published in Print: 2014-09-01

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https://doi.org/10.3139/120.110614