Gold-based bulk metallic glass alloys based on Au–Cu–Si are introduced. The alloys exhibit a gold content comparable to $18\text{-}\text{karat}$ gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds $5\mathrm{mm}$ in the best glassformer. ${\mathrm{Au}}_{49}{\mathrm{Ag}}_{5.5}{\mathrm{Pd}}_{2.3}{\mathrm{Cu}}_{26.9}{\mathrm{Si}}_{16.3}$ has a liquidus temperature of $644\mathrm{K}$ , a glass transition temperature of $401\mathrm{K}$ , and a supercooled liquid region of $58\mathrm{K}$ . The Vickers hardness of the alloys in this system is $\sim 350\mathrm{Hv}$ , twice that of conventional $18\text{-}\text{karat}$ crystalline gold alloys. This combination of properties makes the alloys attractive for many applications including electronic, medical, dental, surface coating, and jewelry.

We report on the solidification of ${\mathrm{Au}}_{49}{\mathrm{Ag}}_{5.5}{\mathrm{Pd}}_{2.3}{\mathrm{Cu}}_{26.9}{\mathrm{Si}}_{16.3}$ bulk metallic glass under various strain rates. Using a copper mold casting technique with a low strain rate during solidification, this alloy is capable of forming glassy rods of at least 5 mm in diameter. Surprisingly, when the liquid alloy is splat cooled at much higher cooling rates and large strain rates, the solidified alloy is no longer fully amorphous. Our finding suggests that the large strain rate during splat cooling induces crystallization. The pronounced difference in crystallization behavior cannot be explained by the previously observed strain rate effect on viscosity alone. A strain rate induced phase separation process is suggested as one of the explanations for this crystallization behavior. The strain-rate-dependent critical cooling rate must be considered in order to assess the intrinsic glass forming ability of metallic liquid.