ABSTRACT: a complex aluminum brass composed of Cu, Zn, AL, B, P, Ce and Sn was designed, and the effects of different Sn contents on the microstructure and properties of the complex aluminum brass were investigated. The results show that the width of EUTECTOID phase increases with the increase of Sn content, but the effect of Sn content on phase composition is not obvious. With the increase of SN content, the tensile strength increases and then decreases, while the hardness and corrosion resistance increase.

Keywords: Complex Brass; Tin Content; casting; mechanical properties; Corrosion Resistance; classification number: TG146.11 document identification number: A article number: 1002-5065(2021)02-0035-3、

Brass is a kind of alloy material based on copper and zinc, which is widely used in heat exchange system and electric transmission system because of its excellent mechanical properties, corrosion resistance and excellent conductivity and thermal conductivity. Pure copper and zinc have limited mechanical properties, poor processability and easy corrosion. Therefore, it is often necessary to add some micronutrient to the Alloy Matrix to adjust its phase composition and improve its mechanical properties and corrosion resistance. AL, BI, FE, MG, MN, Ni, PB, P, CE, SI and Sn were all added into the brass matrix to improve the properties of the alloy. AL AND SI can shift the phase zone of brass to the left, increase the strength of the alloy, and form a dense oxide film on the surface of the alloy to prevent further corrosion The addition of MN has little effect on the microstructure of brass, but it can improve the mechanical properties of brass, the corrosion resistance of brass to chloride in seawater and the heat resistance of the alloy, in addition, Ni can effectively increase the phase ratio and the anti-dezincification cracking ability of brass. At present, there is little research on the effect of Micronutrient addition on the microstructure and properties of complex brass, but Sn can improve both mechanical properties and corrosion resistance in simple brass. Therefore, the effect of Sn content on the mechanical properties and corrosion resistance of brass with more complex composition is not clear.

In this paper, a more complicated brass alloy component (Cu-Zn-Al-B-P-Ce-Sn) has been designed and prepared by casting method, and the addition amount of SN is 0.005 WT. % , 0.01 wt. % , 0.015 WT. % , 0.02 wt. % complex copper alloy. The effect of Sn content on the microstructure and properties of complex copper alloy was studied.

1. Experimental methods

The raw materials used in this experiment include pure copper (3n) , pure zinc (3n) , pure aluminum (3n) , pure Tin (3n) , copper-boron master alloy, aluminum-cerium master alloy and copper-phosphorus master alloy. In the experiment, brass was prepared by melting and pouring. In the melting process, all zinc (over 3% by mass ratio) and some copper were added into the graphite crucible. The mass ratio of copper to zinc was 6:4, the crucible is then placed in a resistance furnace. When the temperature in the furnace rises to 1050 °C, keep the temperature for 5 minutes, add covering agent to the surface of the liquid metal, then add cu-b alloy, cu-p alloy, al-ce alloy and sn to the liquid metal in turn, finally, the remaining copper is added to the liquid metal and kept warm for 5 minutes. A certain proportion of sodium fluoride and cryolite is added to the molten metal before pouring, and then the slag is poured into the baked steel mould to solidify. The composition of the alloy is as shown in Table 1.

The microstructure of the corroded sample was observed by optical microscope, and the processes of rough grinding, fine grinding, polishing and corrosion were followed. The corrosion solution is the aqueous solution of hydrochloric acid and iron trichloride acid, the specific composition is: HCL (30ML) , Fe CL3(2.0 g) , H2o (120ml) . The phase composition of the copper alloy was characterized by XRD. HV-1000 micro-vickers hardness was used to test the hardness of different samples, each sample was tested at 10 points and the average value of the test results was taken. The tensile strength of copper alloys with different composition was tested by universal testing machine. The polarization curves of different samples were measured by Chi660 electrochemical working station. The scanning rate of the polarization curves was 2 mv/s. The three electrode system was used for the determination. The auxiliary electrode was PT Electrode and the reference electrode was SCE, the sample was used as the working electrode, the test area was 10mm 10mm, the solution was 3.5 wt. % D sodium chloride solution.

2. Results and discussion

Fig. 1 shows the microstructure of complex al-brass with different SN contents. It can be seen that the alloy matrix is white and there are a lot of black dendrite structures on the Matrix. It is known from the literature that the black dendritic structure is a phase + phase eutectoid. With the increase of SN content, the black dendrite structure in complex aluminum brass becomes coarser. The SN content promoted the formation of phase + phase eutectoid. The phase composition of copper alloys with different SN contents was analyzed by XRD on the basis of observing the metallographic morphology. The results are shown in Fig. 2. As you can see, the amount of addition to Sn is 0.005 wt. % ~ 0.02 wt. In the range of% , the phase composition of copper alloy is all copper phase. Therefore, it can be inferred that the vast majority of the added elements are solid soluble in copper. The SN content has little effect on the phase composition of copper alloy.

Fig. 3 shows the tensile curves of complex brass alloys with different SN contents. It can be seen that when the SN content varies from 0.005 WT. % increase to 0.015 WT. At% , the ultimate tensile strength of copper alloy is enhanced. When the SN content is further increased to 0.02 wt. At% , the ultimate tensile strength of the alloy decreases. In the aspect of elongation, the elongation of the four copper alloys with Sn content was more than 60% , and the relationship between the elongation and Sn content was 0.01 wt. % & GT; 0.02 WT. . % & GT; 0.015 WT. . % & GT; 0.005 WT. . % . The ultimate tensile strength and hardness of complex copper alloys with Sn content are shown in Fig. 4. It can be seen that the ultimate tensile strength of the alloy increases from about 305 MPA to about 452 MPA with the increase of Sn content, and then decreases to about 384 MPA with the further increase of SN content. The hardness of copper alloy changes with the increasing of Sn content from 0.005 WT. To 0.005 WT. % increase to 0.02 wt. % , the hardness of the alloy is increased from about 80HV to about 100HV.

The results show that the addition of Sn can affect the microstructure, mechanical properties and corrosion resistance of the alloy. However, the effect of Sn addition on the microstructure, mechanical properties and corrosion resistance of the alloy is different. The effects of SN content on microstructure, tensile strength, elongation, hardness and corrosion resistance of complex aluminum brass were studied. The SN content was 0.015 wt. The alloy has the best comprehensive properties at% .

The polarization curves of complex al-brass with different SN contents are shown in Fig. 5. It can be seen that the self-corrosion potentials of all the alloys are near 0.2 v SCE. Therefore, the influence of Sn content on the self-corrosion potentials of cu-based alloys is not significant. However, with the increase of SN content, the self-corrosion current density of cu alloy decreases significantly, and the corrosion resistance of the alloy increases.

3. Conclusion

The effects of SN content on the microstructure, mechanical properties and corrosion resistance of complex aluminum brass containing 7 components were studied by means of experiments. The hardness and corrosion resistance of the alloy increased with the increase of SN content, but the tensile strength and elongation increased at first and then decreased. Considering the effect of Sn content on the microstructure and properties of the copper alloy, 0.015 wt. The comprehensive performance of% Sn addition is better. 

Source: Chinanews.com, by he yuxing