Study On The Glass-forming Ability And Die-casting Performance Of Zr-based BMGs

Zr-based bulk metallic glasses(BMGs)have been widely applied in many high-tech fields for excellent mechanical strength,corrosion resistance and electromagnetic properties,precision members mainly made of consumer electronics are the most common.However,there still exist obvious differences between the dimension and feature of precision members,forming difficulties of various castings are different,for example the thin-walled,the narrow edged,the rings and the bars,thus the study on the die-casting performance of Zr-based BMGs has great theoretical and project value.In this paper,Zr₅₅Cu₃₀Ni₅Al₁₀ and Zr_52.5Cu₂₅Ni_9.5Ti₆Al₇ BMGs were prepared by copper-mold casting.The complex influence of melt temperature and casting pressure on the glass-forming ability(GFA),thermal stability,flowing ability and castings quality were investigated by characterization analysis.Using dynamic viscosity,we re-built the process relationship between the GFA and plastic deformation of supercooled liquid.For different alloys,selecting and designing appropriate features of castings mold,achieved the production of precision members.(1)Zr₅₅Cu₃₀Ni₅Al₁₀ and Zr_52.5Cu₂₅Ni_9.5Ti₆Al₇ metallic glasses with good mechanical property and process performance were selected for experiment and analyzed in composites.The effects of melt temperature and casting pressure on the GFA were studied systematically.It's demonstrated that the GFA of alloys all first increase to the maximum value,then suddenly decrease when temperature grows.Zr₅₅Cu₃₀Ni₅Al₁₀ has stronger GFA,whose critical size can reach 8mm in 1230k?1290k,but the GFA of Zr_52.5Cu₂₅Ni_9.5Ti₆Al₇ has better temperature tolerance.The change of casting pressure within process range couldn't affect the GFA and glass stability nearly.(2)The effects of melt temperature,casting pressure and alloys components on die-casting performance and castings quality were studied significantly.The results show that improvements of melt temperature and casting pressure are beneficial to die-casting performance,but there remains restrictions on the GFA and die-casting performance due to melt temperature.The viscosity effect in different solidification stages determines rheological behaviors and glass transitions.Moderate temperature and high pressure can balance the property superiority of alloys,and achieve amorphous castings with high-quality.(3)Based on the study of the die-casting of amorphous precision members,and comprehensive consideration of shape and size characteristics of the precision members,the pouring position,parting surface,machining allowance,demolding angle and fillet design of the mold were discussed.Finally,a variety of the amorphous precision members were manufactured.Meanwhile,we put forward some solutions for the existing process problems of the large-scale and complex precision members.