Estudo da liga base de Zn-Al-Cu-Mg aplicada na fabricação de jóias folhadas

摘要

The last years, the jewellery industrial sector is becoming of significance importance in the scenario of national and international economy. Brazil is one of the jewels biggest world producer, being the Rio Grande do Sul the leading among all Brazilian states, with a regional distinction for the city of Guaporé witch has more than a hundred jewel factories, where are produced gold and silver jewels and semijewels plated with gold and silver. In spite of it, there are very few literature related to scientific studies in the jewellery area, particularly nationwide. In this context, this research has as a main aim to investigate the Zn-Al- Cu-Mg alloy that has recently applied in fabrication of jewel-plated in order to obtain information about the properties of interest to fabrication and plated processes. The experimental methodology utilized in this work involved the following steps: analysis of superficial defects in gold and silver plated semi-jewel made with Zn-Al-Cu-Mg commercial alloy and as well as the determination of its microstructure and mechanical characteristics; compositional modification of this alloy by the addiction of extra Copper and Magnesium and study of their effects in the alloy properties; and as a final point the evaluation of gold plating capacity of the commercial alloy and the alloy modified with Copper and Magnesium. This study demonstrated that composition variations modified considerably the microstructure of the alloy and consequently its mechanical properties, as well as this plating capacity. The employed characterization techniques CA-CCA (Computer- Aided Cooling Curve Analysis), DTA (Differential Thermal Analysis), Dilatometry and optical and scanning electron microcopies where of fundamental importance to better understand the influence of chemical composition on the microstructure and properties of the Zn-Al-Cu-Mg alloy. However, it was observed that another factor of great influence in the quality of the superficial plated of this alloy is the procedure and quality of cleaning effectuated in the parts for posterior platting process.