effects of grain refining and modification on mechanical properties and microstructures of multielem

1、<p>　　Effects of grain refining and modification on mechanical properties and microstructures of multielem</p><p>　　Abstract. With orthogonal tests the effects of grain refiners and modifiers， Al-10Sr，

2、rare earth（RE） and Al-Ti-5B， on the mechanical properties of Al-Si alloy for automobile cylinder blocks were studied. The best result occurred when the proportion of refiners and modifiers was Al-10Sr = 0.1wt%， RE = 0.3w

3、t%， Al-5Ti-B = 0.8wt%. With SEM and EDS the as-cast microstructures of materials after grain refining and modification were observed and analyzed. Tiny branch-shaped AlSi phase， thin-striped AlC</p><p>　　Key

4、 words： Al-Si alloy； grain refining and modification； orthogonal testing； mechanical properties； microstructures </p><p>　　1.Introduction </p><p>　　With improvement of the living standard and gr

5、owing of the environmental awareness， how to realize the functionality and the comfortableness of automobile and to improve vehicle on energy conservation and pollution reduction further have become the new opportunities

6、 and challenges of automotive industry. It is indicated that[1-3] transportation has consumed 40% of world crude oil. About 15% of the carbon dioxide released from burning fossil fuels has been caused by automobile exhau

7、st. About 60% </p><p>　　2.1 The orthogonal tests </p><p>　　Chemical composition and mechanical properties of the multielement Al-7.5Si alloy used in the present study is shown in Table 1 and Tab

8、le 2. The Al-7.5Si alloy was melted in a silicon carbide crucible using an electric furnace and was kept at 740℃（±5℃）. The grain re？ning and modi？cation of the alloy were done separately by adding Al-10Sr， RE and Al

9、-5Ti-B master alloys at 720℃. The concentration and chemical composition added in cast Al-Si alloy is shown in Table 3 and Table 4. Degassing was done</p><p>　　The alloy was multiplex strengthened using the

10、orthogonal test with 3 factors and 3 levels in accordance with the L9（33） orthogonal conditions （see Table 3） by Al-10Sr， rare earth and Al-Ti-5B for grain refining and modification[11-12]（see Table 4）. The orthogonal te

11、st needed 9 group experiments. </p><p>　　To ensure the accuracy of the experiment， four samples were prepared for each group， and taking the average of two samples as the final performance indicators， which

12、performances were better than two others. Results of the orthogonal test showed in Table 5. A computerized universal testing machine and brinell hardness tester were used for mechanical properties on multielement Al-7.5S

13、i alloy before and after grain re？nement and modi？cation. Tension test specimen showed in Fig.1. Brinell hardness </p><p>　　2.2 The analysis of fitting curve </p><p>　　Grain refining and modific

14、ation had satisfied results （Fig.4）. Most of the eutectic silicon phases have become dot-like and distributes uniformly at the grain boundary. Meanwhile no obvious deterioration was found. It indicated that the interacti

15、on between these three composite modifiers was strengthened. By the way， the tensile strength of the sixth and eighth group samples is lower than the mater alloy， mainly because of deterioration had occurred， eutectic si

16、licon has a large gathering and ch</p><p>　　Figure 5 is the macro-photograph of the sample of master alloy and grain refining and modification alloy， it is obvious that the gas porosity has been greatly impr

17、oved and structures become more compact. </p><p>　　The results of scanning electron microscopy and energy spectrum analysis showed that， as shown in figure 6（a）， all brittle phase Si and phase （α + Si） in th

18、e master alloy were thick bone-like compounds and connected with other metallic compounds （as shown in the figure the A-phase， compounds of five elements Al（MnCuFe）Si and little Ni， Cr， Zn elements） into sheets and bands

19、. Then they were distributed in the grain boundaries of plastic α-phase. In the tensile process， rough gathered brittleness </p><p>　　After grain refining and modification， as shown in figure 6（b）， phase （α+

20、Si） had become small bone-shaped and formed a new ternary compounds AlSiMn. The addition of rare-earth Ce led to form a new B（AlCuCe） phase and changed the shape of AlCu phase from a short rod or a bar into a leaf-shaped

21、 or a feather. Other metal compounds， shown in figure C（AlSiCuZnNiNd） phase， changed their shape from the coarse word shape into bands or bars. The Fe containing phase changed into D（AlSiCuMnFeNiTi） phase， w</p>&

22、lt;p>　　4. Conclusion </p><p>　　Before you begin to format your paper， first write and save the content as a separate text file. Keep your text and graphic files separate until after the text has been form

23、atted and styled. Do not use hard tabs， and limit use of hard returns to only one return at the end of a paragraph. Do not add any 　　1）The orthogonal tests were analyzed with range analysis and significance testing. Usi

24、ng the weighted evaluation value yg* to evaluate the mechanical properties of the master alloy. It was show</p><p>　　2）According to the fitting curve of yg* was drawn the best addition range of these three k

25、inds of single modifiers： Al-Ti-5B： 0.78wt%～0.9424wt%； Al-10Sr and RE： 0.05wt%～0.15wt%. </p><p>　　3）The results of multi-group verifying experiments showed that the average tensile strength σb was 245.52MPa，

26、 the average elongation rate δ was 2.9%， brinell hardness was 86.4HB， which were all in keeping with the requirements of making cylinder blocks. </p><p>　　4）After the grain refining and modification， these b

27、rittle phases reduced in size immensely and distributed by a network. At the same time small branch-shaped AlSiMn phase and leaf-shaped or feathered B（AlCuCe） phase were formed， the other metal compounds had changed into

28、 strips or bars and acted as intercrystalline strengthening to certain degree. Further， porosity was significantly reduced after grain refining and modification. </p><p>　　Acknowledgment </p><p>

29、;　　The authors are highly thankful for the financial support of Mingzhi Technology Ltd. </p><p>　　References </p><p>　　1.Zhang Zhi-min， and Su Xin，“Lightweight aluminum alloy material in the mod

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