An inverted die casting technique has been developed for the rapid and reproducible production of high quality lightweight bulk metallic glass (BMG) castings. Comprehensive processing maps for producing lightweight BMG samples of cross section 3.15 mm x 7 mm and a length of 125 mm were developed as a means of identifying the optimum casting conditions for producing casting of high structural integrity, maximum length and enhanced surface quality. Utilising these maps, Mg65CU25Y10 and

more »

... 0 BMGs were consistently produced using the inverted injection die casting method and a naturally cooled copper mould, by choosing injection parameters that stabilise the molten metal flow front within the mould cavity. Highest quality Mg65CU25Y10 BMG bars were produced in the casting temperature range of 560 C to 580 C and gate velocities in the range of 12.5 to 15 m/s. Highest quality Ca65Mg15Zn20 BMG bars were produced in the casting temperature range of 480 C to 520 C and gate velocities in the range of 13.8 to 14.7 m/s. The casting parameter range for achieving the highest quality castings for the lightweight BMGs examined was found to be practically identical and related to the casting system geometry. The use of higher holding pressures when casting was also found to increase the sample surface quality due to a post-casting consolidation process during sample cooling. As part of the experimental program, critical cooling rate experiments were carried out, whereby the change in casting temperature over time was measured between Tl and Tg. The resulting castings were analysed using x-ray diffraction (XRD). The Mg65CU25Y10 BMG was found to have a critical cooling rate between 49 and 61 C/sec, and may be gravity cast in a copper mould to achieve a completely amorphous structure between 3 and 3.75 mm, or readily cast using the inverted injection method successfully to obtain a thickness of 3.15 mm. The Ca65Mg15Zn20 BMG was found to have a critical cooling rate between 150 and 170 C/sec, and may be cast using the inverted [...]