Selection And Optimization Of Mold Materials For Bulk Metallic Glasses Casting

Bulk metallic glasses（BMGs）have excellent mechanical properties and corrosion resistance,therefore they have been applied in many fields.Among them,the precision parts of consumer electronic products have developed rapidly.However,it’s diffcult to mold fully,because the shape is usually thin and narrow.The molding is related to the casting temperature,the casting temperature and the mold’s shape.Also,it’s connected with the wettability of the melt and the mold,which is connected with the BMG composition and the material of the mold.For two kinds of SIM（Subscribe Identification Module）card molds,we propose that using the length of standard sheet sample to quantify their different formability.On this basis,Zr₅₅Cu₃₀Ni₅Al₁₀（Zr55）and Zr_52.5Cu₂₅Ni_9.5Ti₆Al₇（Zr52.5）alloys are compared by the properties of their formability and GFA.In order to determine the component effect of wettability,we adopt Zr55 and(Zr₅₅Cu₃₀Ni₅Al₁₀)₉₈Er₂ on red copper,Cu-Cr,Cu-Cr-Zr,Cu-Ni-Be,Cu-Co-Be,WC/Cu,H13 steel and quartz by self-making device.The result is analazed by the scanning electron micrograph（SEM）and energy dispersive spectrometer.The surface treatment of the above copper alloys is conducted by pulse detonation plasma technology.The change in the surface morphology and phase are analazed by SEM and X-ray diffraction respectively.Also,the surface microhardness is measured.For two kinds of SIM card molds,their lowest casting temperature for completely forming of Zr55 and Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀ alloys can be determined by spray casting.At this temperature,the standard sheet samples with a section of 0.5×5 mm² are prepared.There are same length of their sample within the range of error,so that the equivalent relationship between the difficulty of forming SIM cards and the length of standard sheet sample is established.Then,according to the length of standard sheet sample and GFA for Zr55 and Zr52.5 alloys at different casting temperature,their formability-GFA diagram is obtained.It can be seen that Zr55 alloy can maintain a larger GFA in a wider casting temperature range,while Zr52.5 alloy can maintain a larger GFA at higher formability.The result can provide a clear basis for selecting suitable components for different production requirements.Zr55 fusant is bonding with H13 steel that was discovered by the wetting test.Obvious interface reaction occurs between Zr55 and H13 steel analazed by EDS.Therefore,it shows that H13 steel is not suitable as a mold material for BMG casting.Another hand,in the rest of mold materials,Cu-Ni-Be shows a higher surface hardness and the most negative wetting behaviour,so that it’s a potential application as mold material for BMG casting.After adding2%Er element to Zr55 alloy,the wettability of all kinds of copper alloys increases slightly.However,the wettability of quartz reduces significantly.It’s meaning that it’s not suitable to add Er element to Zr-based BMG when using copper alloy mold,in contrast using quartz mold.The surface treatment of the above copper alloys is conducted by pulse detonation plasma technology.The result shows that trace of W,W₂N and obvious carbon black appear in the surface of each kind of samples,and melting tumors are formed by local melting.Multiple-time treatments,low capacitance treatment,and process conditions that are not connected to the ground lead to higher density of melting tumors.The surface treatment has an effect on the surface of the copper alloys.The possible area from the surface to the inside is melting area,recrystallization area and recovery area.And,the hardness of the above area increases in turn,therefore the melting area should be the main reason for the decrease of hardness.Red copper and WC/Cu are suitable for multiple-time treatments.Red copper,Cu-Cr,Cu-Cr-Zr and Cu-Co-Be are suitable for processing conditions that are not connected to the ground.The above copper alloys are not suitable for high capacitance treatment.