Effect of hottest titanium on mechanical propertie

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Effect of titanium on the mechanical properties of alsi7mg0.3 alloy the effect of titanium on the microstructure and mechanical properties of alsi7mg0.3 alloy was studied. When the content of titanium exceeds 0.12%, the grain of aluminum alloy is no longer refined, but the impact toughness and elongation decrease sharply, the tensile strength increases slowly, and the hardness changes little. The change of mechanical properties may be caused by the appearance of acicular titanium phase. The optimum titanium content of alsi7mg0.3 alloy should be in the range of 0.08% ~ 0.10%. At this time, the iron content is close to 0.18%, and the alloy still maintains high impact toughness and plasticity

key words: alsi7mg0.3 alloy optimum titanium content mechanical properties refining effect

high strength and high toughness alsi7mg0.3 alloy is widely used to manufacture complex load-bearing parts in aerospace, aviation, automobile, transportation and other industries

Since the 1950s, in order to further improve the mechanical properties of alloys, Al Ti or Al Ti B master alloys have been commonly added to refine aluminum grains [1, 2]. For example, the American ASTM standard specifies that the titanium content ranges from 0.04% to 0.20%. China also stipulates that the titanium content should be 0.08% ~ 0.20%. However, the experience provided by production shows that the amount of titanium in the range of 0.02% ~ 0.15% has satisfactory grain refinement effect [3, 4]. Up to now, the research on the refinement effect of titanium has mostly focused on Al Cu single-phase alloys, and few have involved Al Si alloys [3]. Therefore, the purpose of this paper is to clarify the refining effect of titanium on a and its influence on the mechanical properties of lsi7mg0.3 alloy, and to explore the optimal range of titanium content

1 test method

alsi7mg0.3 alloy is melted in 500 kg resistance furnace under the production conditions of automobile hub factory. Degasify with nitrogen at 690 ~ 710 ℃, modify with alsr10 alloy, and pour the wheel hub and Y-shaped test block (20 mm) after standing for 10 min × 80 mm × 220 mm)。 The metal mold temperature is controlled at about 250 ℃. The amount of titanium and iron shall be adjusted with Al Ti alloy and aluminum ingots of different grades according to the test scheme. Table 1 lists the composition range of the test alloy. Table 1 Composition of alsi7mg0.3 alloy for test (mass fraction/%)

element simgfetisr6.80 ~ 7.500.28 ~ 0.330.08 ~ 0.270.07 ~ 0.300.06 ~ 0.08

the sample is subject to solution treatment in a continuous heat treatment furnace with the wheel hub (535 ℃) × 6 h) and aging treatment (135 ℃ × 8 h)。 Take tensile test bar and notchless impact test block (10 mm) from Y-shaped test block × 10 mm × 55 mm)。 Take samples from the fracture surface of the sample to observe the metallographic structure of the alloy

2 results and analysis

2.1 mechanical properties

Figure 1 shows the effect of titanium content on the tensile strength, elongation and impact toughness of alsi7mg0.3 alloy with different iron content. Once the titanium content exceeds 0.12%, the elongation and impact toughness of the alloy begin to decrease. When it increases to 0.20%, the elongation and impact toughness decrease by 20% and 30% respectively, and the tensile strength slightly increases by about 5%, but the hardness does not change significantly. It can be seen that the titanium content should not exceed 0.12%, which is close to the lower limit of ASTM and Chinese aluminum alloy specifications

Fig. 1 Relationship between titanium content and mechanical properties of alsi7mg0.3 alloy

iron content also has a significant effect on impact toughness and plasticity of alsi7mg0.3 alloy. When the iron content increased from 0.08% to 0.21%, the impact toughness and elongation decreased by 25% and 30% respectively, and the strength increased by 10%. The change range was roughly the same as that of titanium

2.2 metallographic structure

Fig. 2 Comparison of metallographic structure of alsi7mg0.3 alloy with different titanium content. The amount of titanium increased from 0.08% to 0.21%, and no obvious changes in the morphology and size of aluminum dendrites were observed. The size and distribution of granular silicon phase were not affected. When the titanium content exceeds 0.12%, the α- Light red and or massive titanium phases are found in Al dendrites, as shown by arrows 1 and 2 in the figure. This effect of titanium is the same as that reported in literature [3, 5]. The amount of titanium increases to 0.1. This guide provides designers and designated personnel with more than 0% guidance on the best environmental choice when selecting building materials and components, and the grain size of aluminum will no longer decrease

a. 0.08%ti ~ 0.18%feb. 0.21%ti ~ 0.18%fe

Fig. 2 metallographic structure of alsi7mg0.3 alloy with different titanium content (as heat treated) × 100 arrow 1 - acicular titanium phase; Arrow 2 - massive titanium phase

3 discussion

it is generally considered that the grain refinement of titanium is caused by peritectic reaction between aluminum and TiAl3. These early studies [1, 2] are limited to Al Si binary system. Therefore, the following view is drawn: peritectic reaction can be carried out only when titanium exceeds 0.15%, and TiAl3 can act as aluminum crystal nucleus to refine grains. This critical value does not conform to the production practice (0.02% ~ 0.15%), nor is it confirmed by this work. This difference is related to the alloy composition. In 1987, mondolfo's more detailed study [6] confirmed that Fe means that the method of general election cannot be implemented in the election of the fifth executive seat of the Hong Kong Special Administrative Region in 2017. Mn, Zn, Mg, Cu, etc. successively reduce the peritectic reaction temperature of Al Ti and the solubility of titanium in molten aluminum. Mg and Cu are the strongest, which can reduce the solubility of titanium to less than 0.08%. If boron is present, the solubility of titanium decreases to 0.03%. Therefore, the critical value of titanium decreased to below 0.10%. The alsi7mg0.3 alloy used today contains Si and Mg, and its combined effect on the solubility of titanium remains to be studied. As the main processing machine, the recycled plastic granulator will have a large customer base. According to the production statistics, the grain refinement effect can be shown when the titanium content is less than 0.08%. As for why the amount of titanium is greater than 0.12% and the refining effect is no longer increased, the following discussion can be made

the author used JCXA-733 spectrometer to measure that the titanium content in alsi12cumg alloy matrix is about 0.12% ~ 0.16%, with an average of 0.14%, which is close to the value published in literature [6]. If the amount of titanium exceeds this value, titanium will appear in the form of acicular or massive alsiti intermetallics, as shown by the arrow in Figure 2B

the amount of titanium is between 0.08% and 0.10%. As the grain is fully refined, the impact strength and plasticity of the alloy are improved [4 ~ 6]. On the contrary, when the amount of titanium exceeds 0.12%, the grain refinement stops gradually, and acicular or massive intermetallic compounds are precipitated, which reduces the impact toughness and plasticity of the alloy and weakens the increase of strength. Therefore, the optimum titanium content of 0.08% ~ 0.10% can ensure the maximum toughness and plasticity of the alloy

in order to ensure that the alloy has sufficient toughness and plasticity, many factories often focus on reducing the iron content, ignoring the duality of titanium role, and often adopt the method of low iron and high titanium, which brings a lot of inconvenience to the production operation and management, and also increases the production cost. On the contrary, the titanium content is reduced to 0.08% ~ 0.10%. Even if the iron content is close to 0.18%, the impact toughness of the alloy can reach 40 j/cm2, the elongation remains at 12%, the strength is also very high, the cost is reduced, and the on-site process and management are convenient

4 conclusion

alsi7mg0.3 alloy has the best titanium content of 0.08% ~ 0.10%. If it is too high, the toughness and plasticity of the alloy will decrease sharply

author unit: China Textile University


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