Preparation and characterization of Au-Pt alloy with ultra-low magnetic susceptibility

Gold-platinum alloy is considered as an ideal material for testing masses in gravitational wave detection. Nevertheless, systematic studies on the microstructure and properties of Au-Pt alloys, which are essential for preparing test masses that meet the requirements of space gravitational wave detection, are currently absent. To this end, this study fabricated three types of Au-Pt alloys (Au-20Pt, Au-26Pt, and Au-32Pt) and systematically investigated the influence mechanisms of Pt content, cold deformation, and precipitation phase on the microstructure, mechanical properties, and magnetic properties of Au-Pt alloys. The experimental process encompassed cold rolling deformation ranging from 40 % to 80 % for each alloy and a specific aging treatment study at 550 °C to 850 °C for the Au-26Pt alloy.

The results demonstrate that increments in Pt content led to hardness increases and decreases in absolute value of magnetic susceptibility ($\left(\chi \right)$) of the Au-Pt alloys; meanwhile, as the cold rolling deformation escalates, both the hardness and magnetization rate $\left(\chi \right)$ of the Au-Pt alloys will increase. Aging treatment causes the precipitation of the Pt-rich phase from the alloy matrix. The higher the aging temperature is, the lower the hardness of the Au-26Pt alloy will be, and the $\left(\chi \right)$ of the alloy reaches its lowest value of 9.33 ppm after aging at 650 °C for 5 hours. The aforementioned findings can furnish theoretical bases and guiding opinions for the design and preparation of ultra-low magnetic test masses for gravitational wave detection.