ABSTRACT: in the process of H62 brass production, when cooling water is used, the cooling water flow will affect the microstructure and properties of H62 and the final cold rolled coil. In this paper, the influence of different cooling water flow rate on the microstructure and properties of H62 and further on the properties of cold rolled strip are introduced. Key Words: Cold Rolling Property; H62 BRASS; Cooling Water, author: Luo Qirong ZHONGTU classification number: TG335.11 Literature Identification Number: a article number: 1002-5065(2018)19-0159-2

1.Performance, application and composition of H62 brass

(1) H62 brass has high strength, good plasticity in hot state, good plasticity in cold state, good machinability, easy welding, good corrosion resistance. Used to make all kinds of pins, rivets, nut washers, guided wave tube, clamp plate, ring parts, and radiator parts, ship industry, paper industry parts and so on 

(2) simple brass organization: zinc solid solution in a large amount of copper. In solid state, six phases

Brass is generally hard and brittle at room temperature, but at high temperatures it is softer than brass 

(3) H62 brass composition

2.Introduction of traditional production technology

At present, the process of H62 brass production by hot rolling is heating, hot rolling, coiling and milling. The disadvantage of this technology is that the hot rolled coil must be uncoiled twice when milling, which affects the production and has low efficiency. In order to increase productivity, we have to

The hot rolled strip can not be milled directly, but because the temperature of hot rolled strip is very high, it needs cold water to milled. From the view of production practice, the process of strong cooling with water has a great influence on the following rolling performance of H62. In this paper, the effect of water cooling rate on the properties of cold rolled strip is studied. H62 BRASS HOT rolling process, 1 out of the furnace temperature is generally about 820 °C, ingot from the appearance of color to be uniform, not white. 2 The hot rolling passes of typical H62 brass are arranged as follows: unit mm, 240-220-183-150-120-100-81-57-42-25-21-16, the finishing temperature of strip is generally over 550 °C. 3 Roll Cooling Condition: The emulsion cooling concentration is 1.2% , and the flow rate is cycled five times per hour.

3. The testing process

(1) the flow of the cooling device is cooled according to 2000m3/h, and the hardness of hot rolled strip is measured at 120HV ~ 140HV, the tensile strength is 410 ~ 435MPA, and the elongation is 27% ~ 30.5% . This hardness value range is roughly semi-hard, generally speaking, the hardness value after hot rolling in 80HV ~ 90HV. The metallograph of a typical hot rolled coil during cooling at 2000m3/h is as follows:

The drawing above shows the pass table of 100x hot rolling direction (the black part is the phase, the content is high) when the hot rolling 2000m3/h is cooled (actual) .

Through Table 2 analysis, Cold Rolling Force is very large, the material is not easy to deformation. Moreover, the shape of the plate is obviously bad, and the lateral tolerance of the coil is large, reaching 63um in severe cases. As a result, rough rolling is difficult and there are many passes. It takes 8 passes to roll the Strip from 14.0 mm to 3.00 mm. The reduction is very small, the reduction from 6.2 mm to 5.4 mm in the fourth pass is less than 20% , but the rolling force is up to 1200 tons, and the rolling force is very large. (2) change the flow rate of cooling water to 1000m3/h, ensure the strip to cool to 400 °C in a certain time, then increase the water cooling rate to 2000m3/h, test the physical properties of the Strip: tensile strength 350Mpa ~ 380MPA, hardness 89 HV, extension 35% ~ 50% . Changing the flow rate of cooling water to 1000m3/h, ensuring that the strip is cooled to 400 °c within a certain period of time, and then increasing the water cooling rate to 2000m3/h, the phase diagram is as follows (the phase content decreases) :

Change the water flow rate to 1000m3/h, ensure the Strip to cool to 400 °C in a certain time, then increase the water cooling rate to 2000m3/h, cold rolling pass list (actual) .

As can be seen from table 3, the number of passes has been reduced and the rolling force has been reduced, with tolerances and transverse wedge improvements up to 10um. The effect is obviously improved, and the edge cracking phenomenon is also gone.

4.Conclusion

The cold rolling performance of H62 can be improved greatly by adjusting the cooling flow and speed without affecting the efficiency of mill and milling surface. Cause Analysis: At high temperature, because the cooling rate is very fast phase can be retained, resulting in cold rolling deformation is not easy. If the cooling rate is lowered to allow sufficient time for the transformation to pass through the phase diagram, the reduction can be clearly seen, thus significantly improving the cold rolling. In addition, the elongation of al-mg alloy can reach 460% . In this way, al-mg alloy has low yield strength. In the course of their research, some researchers have found that the deformation uniformity of aluminum-magnesium alloy is not very consistent when it deforms, and in some relatively coarse crystals, it's easy to surround some of the smaller crystals. As the degree of extrusion increases, local dissonance will occur during the deformation process, and this dissonance will slowly transform into some smaller crystal particles. After the study, the researchers concluded that this deformation process, due to the size of the crystal particles there is a certain difference, in the time of deformation will produce local uneven deformation. Chinese researchers, such as Liu Ying and Chen Wei, have found that during the process of ECAP, the elongation of al-mg alloy increases as the crystal changes, and the degree of yield will slowly decrease, but the actual change in tensile strength is not very obvious. As the frequency of extrusion increases, the size of the crystal will change accordingly, and the yield will also decrease. Other researchers have analyzed the microstructure of aluminum-magnesium alloys, and determined that the average size of the crystals is about 300um, and the minimum size is about 50um, after refinement, the grain size can be kept between 4um and 10um, the strength of the alloy increases from 100MPa to 250MPA, and the elongation increases from 1% to 4% , and the increase rate reaches 300% . Although a great deal of work has been done in the field of ECAP processing technology in China, the research work on wrought aluminum-magnesium Alloy is still at the preliminary research and development stage, this aspect of the problem requires a great deal of research by the relevant staff.

5.Outlook

At present, compared with some developed countries in the world, China still has a relatively obvious gap in the processing industry of Non-ferrous metal. Furthermore, in recent years, the economic input in this field has increased, but in the overall effect is not very obvious. The potential of semi-solid metal forming and ECAP processing technology is relatively large, and semi-solid technology is also widely used in the United States, Japan and other relevant countries, china's technical research in this area also needs to continue to improve. Give full play to China's resource advantages, in the future development process, through energy-saving, efficient, green environmental protection technology, China will be in this regard a new breakthrough technology.

6.Conclusion

Through the analysis and study of the processing technology of Non-ferrous metal, we can see that our country needs to continue to enhance the research and resources investment in Non-ferrous metal in the process of technological development, non-ferrous metal continues to develop its ECAP processing technology so that it can compete in the industrial landscape for years to come. Ref. [1] Chen Changjun, Chen Chuncan, Zhao Jingshen. An analysis of the current situation of industrial technical service in Non-ferrous metal industry. Non-ferrous metal, 2017,46(01) : 1-4. [2] Lee Yiu Ching. Current situation and development trend of Non-ferrous metal extrusion technology. Windows and doors, 2015(02) : 188. [3] Song Qunling. Teaching reform based on the course of working process "Non-ferrous metal plastic processing technology" [ J ] . Chinese out-of-school education, 2011(02) : 99. [4] significant progress has been made in the construction of key laboratories of the Ministry of Non-ferrous metal and materials processing. Journal of Guilin Institute of Technology, 2007(01) : 143. 

Source: Chinanews.com, by Luo Qirong

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