Optimizing mechanical properties of laser-welded gold alloy through heat treatment

Abstract

Objective. The goal of this work was to improve the mechanical strength of laser-welded gold alloy with age-hardenability at intraoral temperature. Methods. The gold alloy was cast conventionally in plate patterns (0.5 mm×3.0 mm×20 mm). After bench-cooling the mold to room temperature (as-cast state), transverse sections of the plate were made at mid-span. They were butted against one another and welded using Nd:YAG laser (current: 320 A; time: 10 ms; spot diameter: 1 mm). Three laser pulses were applied from both sides to cover the joint width (3.0 mm) of the specimens before or after solution heat treatment at 700 °C/5 min. Uncut control specimens (non-welded) were also prepared. After solution treatment, two different heat treatments were given the laser-welded specimens: high-temperature aging at 250 °C/15 min, or intraoral aging at 37 °C/3 days. Control specimens underwent all of the heat treatments after solution treatment. Tensile testing was conducted at a crosshead speed of 2 mm/min and a gauge length of 10 mm. Results. Solution treatment of the gold alloy before laser-welding did not improve the mechanical strength of laser-welded gold alloy after high-temperature aging or intraoral aging. The joint strengths of laser-welded gold alloy were improved only by solution heat treatments after laser-welding and subsequent aging treatment at high or intraoral temperatures. Significance. The results of this study indicated that laser-welded cast gold alloy prostheses aged at high or intraoral temperatures produce high strength when they are solution-treated after laser-welding.