Bismuth widely used to formulate a variety of different uses low melting point alloy with other metals, such as Bi-Pb-Sn-Cd alloy is used in formulating the fusible element, and solder mold, Bi-Sb-Sn-Pb alloy for casting printing lead word; Bi-Pb-Sn solder alloy used in the formulation.

First, the preparation of fusible components and solder

Fusible components and solders are mainly used in electrical fuses and automatic devices. It is generally considered that the melting point is below 200 ° C and belongs to a low melting point alloy. When the tin content is 48% or less, the volume shrinks during solidification, and when the content contains 55% or more, the volume expands during solidification, and when the content contains 48% to 55%, the volume changes little during solidification. The alloys for preparing fusible solders are mainly Wood alloy, Newton alloy, 58 alloy, 47 alloy, etc. The chemical composition and physical properties are listed in Table 1.

Table 1 Composition and properties of bismuth-based fusible solder alloy

Second, the preparation of printed typeface

The typeface alloy made of enamel can be clearly and completely displayed even with very precise graphic lines and very thin strokes. The composition of the printed lead alloy containing bismuth is shown in Table 2.

Table 2 Composition of bismuth-containing printed lead alloy (%)

Third, the preparation of bismuth-based mold alloy

The low melting point mold alloy is used to make a thin plate cold stamping die, which can press copper , aluminum , steel, stainless steel and other plates, and the thickness of the steel plate can reach 3 mm. Used for stretching, bending and forming of sheets. The use of low melting point alloy mold, no mold steel, simple and rapid mold formation; low mold cost, fast update; mold does not need to be adjusted, no processing; mold can be re-melted after use, alloy can be used repeatedly; due to rapid mold formation, Greatly reduce mold stacking space.

Foreign research and use of low melting point mold alloys are very important. Many large aircraft and automobile companies have experts engaged in this research work. Since the 1970s, the promotion and use of low melting point alloy molds in China has been rapidly developed.

The low melting point mold alloy should have the following properties, low melting point, easy to melt, convenient mold making; high alloy strength, long service life of the mold; good flow performance, strong filling ability after alloy melting, clear mold; low expansion and contraction rate of alloy The mold forming precision is guaranteed; the alloy and the standard sample are not adhered, and the parting mold is easy; the alloy is non-toxic and does not pollute the environment.

The Bi-Sn-based alloy composed mainly of bismuth and tin has two kinds of binary, ternary, and plural kinds, and has low melting point, high strength, good fluidity, small expansion and contraction rate, and little metal oxidation loss after remelting.

Bi-Sn-based mold alloys are often added with metal elements such as lanthanum , cadmium , zinc and indium to form a multi-component alloy. Cadmium can refine the grain of the alloy and increase the strength, but cadmium is toxic, and its oxide is volatile and expensive. Lead can reduce the melting point of the alloy and partially replace the expensive tin. However, after adding lead, the thermal conductivity of the alloy is lowered, the fluidity is deteriorated, zinc has the effect of improving the strength of the alloy, low oxidation, and it is difficult to control the alloy composition after melting: The strength of the alloy, but its melting point is increased; indium can lower the melting point of the alloy, but it is expensive.

Table 3 lists the composition and properties of several bismuth based mold alloys:

Table 3 Composition and properties of base mold alloy

Among the seven alloys listed in Table 3, mainly the first two, No. 1 is Bi-Sn binary alloy, No. 3 and No. 4 are essentially developed on the basis of No. 1, and their composition and properties are compared with No. 1 alloy. Approximate; No. 2 is a quaternary alloy, known abroad as a Wright alloy, which is also a major low-melting mold alloy due to the reduced content of heavy metal tin and antimony, while Alloys No. 5, No. 6, No. 7 are also Developed on the basis of Alloy No. 2, their chemical composition and physical properties are similar to some extent. Both the No. 1 alloy and the No. 2 alloy have been studied in detail at home and abroad.

The mechanical and physical properties of Bi-Sn binary alloy (No. 1) are as follows:

Cold expansion of the alloy: When the alloy is condensed into a solid state by liquid, the volume is slightly expanded. By measurement: 2 minutes after condensation, the test bar (12.7×12.7×254 mm) is expanded by 0.0158 mm; after condensation for 1 hour, the test bar is expanded by 0.0152. Millimeter; after 5 hours of condensation, the test bar is expanded by 0.0127 mm.

The strength of the alloy; the strength of the alloy decreases with increasing temperature. When the temperature rises from 26 ° C to 50 ° C, the tensile strength of the alloy drops from 5880 Pa to 4263 Pa; when the temperature rises from 20 ° C to 50 ° C, the compressive strength decreases from 6046.6 Pa to 3959.2 Pa.

The relationship between the load operation time and the hardness of the alloy, the hardness of the alloy decreases with the extension of the load duration. When the test conditions are a diameter of 5 mm, a sample load of 612.5 N, a temperature of 19 ° C, and a duration of 15 seconds, the hardness of the alloy is 23.1; at 30 seconds, it is 20.1; at 1 minute, it is 17.0; at 2 minutes, it is 14.0; at 3 minutes, when it is 5 minutes It is 13.0; it is 12.2 at 5 minutes.

Performance stability after repeated casting of alloy: When the sample diameter is 10 mm, the load is 2,450 N, for 60 seconds, and the temperature is 19 °C, the hardness changes are: within 2 times, the hardness is 21.9; within 35 times, the hardness is greater than 20; Within the second time, the hardness is greater than 19.

The Bi-Pb-Sn-Cd quaternary alloy has a low melting point and good fluidity, but its hardness is also low.

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