Work

Microstructure Modification of Purple Gold Intermetallic Compound Through Si–Co Additions and Copper Mold Casting

Year: 2026

Type: article

Abstract: The brittleness of 18-karat purple gold originates from the AuAl2 intermetallic compound. This study investigates the microstructural modification of the AuAl2 intermetallic compound by adding silicon (Si) and cobalt (Co) and by rapid solidification in copper molds. The samples with alloy additions from a traditional investment casting were compared with copper mold casting for grain boundary characteristics using SEM, EBSD, and TEM. SEM micrographs showed a reduction in grain size of copper mold casting from approximately within 150–200 μm to within 12–20 μm. EBSD showed a narrow grain size distribution in the Si–Co-modified alloy than in the Si-modified alloy, using the copper mold casting technique. TEM observations show that grain boundaries were closely packed, with ~80 nm-sized voids. XRD confirmed that all alloys retained the AuAl2 intermetallic phase, with peak broadening in the modified and fast-cooling samples indicating crystallographic refinement. These results confirm that Si-Co additions with a fast cooling rate effectively refine the microstructure of the AuAl2 intermetallic compound, making the alloy less brittle while preserving the purple gold color.

Source: Metals

DOI: 10.3390/met16030355

Authors: Adiruj Peerawat, Jingran Yang, Jinkang Lu, Jie Yu, Kageeporn Wongpreedee

Institutions: Srinakharinwirot University, Kunming University of Science and Technology

Language: English

Topic: Metallurgical and Alloy Processes

Subfield: General Materials Science

Field: Materials Science

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $3,137

Funders: Ministry of Education of the People's Republic of China, Kunming University of Science and Technology