The effects of Zn and Si on the hardness, tarnish
resistance and microstructures of experimental Ag-
Cu-Zn-Si alloy were investigated by means of vick
ers hardness, tarnish testing, optical and scanning
electron microscopy (SEM) and energy dispersive
spectroscopy (EDS). The various compositions of 935
sterling silver alloys produced by different casting
techniques, investment (lost wax) process and metal
mould casting, were compared. An induction casti
ng machine with a vacuum system was used for
investment casting at 1,025°C with the mould temp
erature at 600°C whereas a LPG/oxygen single flame tip
torch was used for the metal mould process. Vicker
s hardness of the samples produced via metal mould
casting has higher hardness than that of the sampl
es obtained by investment casting. The hardness of
standard 935Ag sterling samples produced by metal mould casting was around 66 HV while it was around
56 HV for the investment cast samples. The increase in ha
rdness is related to differences in the cooling rate
of solidification rather than to the addition of thir
d elements. The tarnish test was performed by immersing
the samples in 0.1% Na
2
S solutions for 15-180 min. To specify th
e color change by ta
rnishing, the surface
color differences (DE*) were measure
d according to the Commission Inte
rnational d’ Eclairage (CIELAB)
standard. It was found that the tarnis
h resistance was improved with high a
dditions of elements especially Si.
Furthermore, Si addition plays an important role
in a complete microstructural modification, which
coincides with the increase in tarnish resistance of st
erling silver alloys, in terms of transforming a lamellar
eutectic structure to a predominan
tly Cu-Si continuous structure.
The effects of Zn and Si on the hardness, tarnish resistance and microstructures of experimental Ag-Cu-Zn-Si alloy were investigated by means of vickers hardness, tarnish testing, optical and scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The various compositions of 935 sterling silver alloys produced by different casting techniques, investment (lost wax) process and metal mould casting, were compared. An induction casting machine with a vacuum system was used for investment casting at 1,025°C with the mould temperature at 600°C whereas a LPG/oxygen single flame tip torch was used for the metal mould process. Vickers hardness of the samples produced via metal mould casting has higher hardness than that of the samples obtained by investment casting. The hardness of standard 935Ag sterling samples produced by metal mould casting was around 66 HV while it was around 56 HV for the investment cast samples. The increase in hardness is related to differences in the cooling rate of solidification rather than to the addition of third elements. The tarnish test was performed by immersing the samples in 0.1% Na2S solutions for 15-180 min. To specify the color change by tarnishing, the surface color differences (DE*) were measured according to the Commission International d’ Eclairage (CIELAB) standard. It was found that the tarnish resistance was improved with high additions ขององค์ประกอบโดยเฉพาะอย่างยิ่งใน นอกจากนี้ ซีนี้มีบทบาทสำคัญ ใน microstructural เปลี่ยนสมบูรณ์ ซึ่ง กรุณาเพิ่มในพจน์ความต้านทานของเซนต์โลหะผสมเงิน erling ในแปลงแบบ lamellar โครงสร้าง eutectic predominantly Cu ในโครงสร้างอย่างต่อเนื่อง
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