CN102392151B - Method for refining SrMgSn phase in Mg-Sn-Sr magnesium alloy by adding Ca - Google Patents

Abstract

A method for refining SrMgSn phase in Mg-Sn-Sr magnesium alloy by adding Ca is realized by adding Mg-Ca intermediate alloy into Mg-Sn-Sr magnesium alloy. Specifically, Mg-Sn-Sr magnesium alloy is formulated according to a certain proportion, melted and heated to 720-740 DEG C under protection of flux or gas, and added with Mg-19wt.% Ca intermediate alloy, wherein addictive amount of Ca accounts for 0.1-0.25wt.% of a gross weight of a furnace charge. The method can effectively refine crude SrMgSn phase in Mg-Sn-Sr magnesium alloy and improve performance of Mg-Sn-Sr magnesium alloy, thereby accelerating industrialization application process of the Mg-Sn-Sr magnesium alloy.

Description

Method of adding Ca to refine SrMgSn phase in Mg-Sn-Sr series magnesium alloy

technical field

The invention relates to a method for adding Ca to refine the SrMgSn phase in a Mg-Sn-Sr series magnesium alloy, belonging to the field of metal materials and metallurgy.

Background technique

As the lightest commercial metal engineering structural material, magnesium alloy is known as the "21st century" because of its light specific gravity, high specific strength and specific stiffness, strong damping and vibration reduction, excellent liquid forming performance and easy recycling. Green Structural Materials". However, at present, due to the poor high-temperature creep resistance of existing magnesium alloys, the long-term working temperature cannot exceed 120°C, making it impossible to manufacture automotive transmission parts that require high high-temperature creep performance, thus greatly hindering the further development of magnesium alloys. application. It is precisely because of this that the research and development of heat-resistant magnesium alloys for automobiles with high-temperature creep resistance at home and abroad have been highly valued, and Mg-A1-Si, Mg-A1-RE, and Mg-A1 have been trial-produced successively. -Ca, Mg-A1-Ca-RE, Mg-A1-Sr, Mg-A1-Sn, Mg-Zn-A1, Mg-Zn-RE, Mg-Zn-Si, Mg-Zn-Sn and Mg-Sn - Ca and other series of heat-resistant magnesium alloys. Among these heat-resistant magnesium alloys that have been trial-produced and studied, the Mg-Sn-Sr series magnesium alloy is considered to be a promising one due to its advantages in high temperature performance, low cost and good corrosion resistance. A new generation of high-temperature creep-resistant magnesium alloys [Hongmei Liu, Yungui Chen, Haofeng Zhao, Shanghai Wei, Wei Gao, Effects of strontium on microstructure and mechanical properties of as-cast Mg-5 wt.%Sn alloy, Journal of Alloys and Compounds, 2010, 504(2): 345-350]. Compared with other heat-resistant magnesium alloys, the heat-resistant strengthening mechanism of Mg-Sn-Sr magnesium alloys is mainly achieved by introducing low-cost alloying elements Sn and Sr to form SrMgSn phases at grain boundaries and within grains. Since the SrMgSn phase is quite stable below 300°C, the Mg-Sn-Sr series magnesium alloy has high high temperature creep resistance. It is also because of the advantages of Mg-Sn-Sr series magnesium alloys that people have paid extensive attention and paid great attention to the research and development of Mg-Sn-Sr series heat-resistant magnesium alloys in recent years. Active research has been carried out on this. For example, Li Shicheng found that the steady-state creep rates of Mg-5Sn-2Sr and Mg-5Sn-3Sr ternary magnesium alloys at 175°C and 35MPa were 3.93×10 ^-7 s ^-1 and 3.67×10 ^-7 respectively. s ^-1 , showing high high temperature creep resistance [Li Shicheng, Chen Yungui, Xiao Sufen, Tang Yongbai, Wang Qing, Zhao Yuanhua and Ding Wucheng, Microstructure and properties of as-cast Mg-5Sn-(0~3)Sr alloy , Special Casting and Nonferrous Alloys, 2011, 31(4): 369-372]. At present, although a certain amount of research has been carried out on Mg-Sn-Sr series magnesium alloys at home and abroad, its popularization and application is still limited to a certain extent due to the poor comprehensive mechanical properties of the alloy. As mentioned above, the heat resistance strengthening mechanism of Mg-Sn-Sr magnesium alloys is mainly achieved by introducing low-cost alloying elements Sn and Sr to form SrMgSn phases at grain boundaries and within grains, but because the formed SrMgSn phase is relatively coarse, The coarse SrMgSn phase will become the source of cracks and lead to the decrease of the creep resistance of the alloy. Therefore, refining the SrMgSn phase is considered to be one of the key factors to improve the creep resistance of Mg-Sn-Sr series magnesium alloys. It is well known that alloying and/or microalloying is one of the effective methods to refine and/or modify second phases in engineering alloys. But so far, there is no literature report on the investigation of the coarse SrMgSn phase in Mg-Sn-Sr alloys refined by alloying and/or microalloying.

Contents of the invention

The purpose of the present invention is to solve the problem that the existing Mg-Sn-Sr series magnesium alloys have coarse SrMgSn phases that affect the performance of the alloys, and propose a method of alloying and microalloying, including its refinement process, to achieve refinement. The purpose of the coarse SrMgSn phase in the Mg-Sn-Sr series magnesium alloy is to improve the mechanical properties of the Mg-Sn-Sr series magnesium alloy and accelerate the industrial application process of this series magnesium alloy.

In order to achieve the above object, the present invention proposes a method and refinement process of adding Ca to refine the coarse SrMgSn phase in the Mg-Sn-Sr series magnesium alloy. In the Mg-Sn-Sr series magnesium alloy, by adding Mg-19wt%Ca The method of intermediate alloy is used to refine the coarse SrMgSn phase in the Mg-Sn-Sr series magnesium alloy. At the same time, the addition of Ca not only has the above-mentioned refining effect, but also has the effect of strengthening the alloy.

The refinement process of the present invention is as follows: Under the protection of flux or gas, melt the Mg-Sn-Sr magnesium alloy according to the corresponding composition ratio and then heat it up to 720-740°C, add Mg-19wt.%Ca master alloy; Ca is added The percentage of the amount to the total weight of the charge is 0.1-0.25wt.%, adding method: bake the Mg-19wt.%Ca master alloy at 100-150°C for 15-30 minutes, and then quickly press it into the alloy below the liquid level with a pressure ladle About 2-6 minutes, after stirring, heat up to 730-750°C, then refine with C ₂ Cl ₆ refining agent for 5-10 minutes, after refining, stir the alloy melt and stand at 740°C for 10-15 minutes, let stand After the completion, the surface scum is removed, and then casting is carried out.

The mechanism of using this method to refine the SrMgSn phase is that the Ca element has a larger atomic radius than the Sn element (Ca: 0.197nm; Sn: 0.141nm). When Ca is added to the Mg-Sn-Sr magnesium alloy, due to the low solid solubility of Ca element in the magnesium matrix, it will be enriched at the solid-liquid interface during solidification, thereby hindering the diffusion of Sn atoms, and eventually leading to SrMgSn phase refinement. In addition, adding a small amount of Ca will form the CaMgSn phase in the Mg-Sn-Sr magnesium alloy, because the crystal structures of the CaMgSn phase and the SrMgSn phase are both Orthorhombic/Pnma structures, and the lattice constants of the two are similar (the lattice constant of the CaMgSn phase : a=7.86, b=4.66 and c=8.74; the lattice constant of the SrMgSn phase: a=8.18, b=4.92 and c=8.75), making the lattice mismatch between the CaMgSn phase and the SrMgSn phase less than 6%, so The CaMgSn phase will become the heterogeneous nucleation core of the SrMgSn phase during the solidification process of the Mg-Sn-Sr magnesium alloy, thereby further refining the SrMgSn phase.

Description of drawings

Figure 1A and Figure 1B are the metallographic structure comparison diagrams of Mg-3Sn-2Sr magnesium alloy without adding Ca and adding Ca and refining:

Fig. 2A and Fig. 2B are comparison diagrams of metallographic structure of Mg-5Sn-3Sr magnesium alloy without adding Ca and adding Ca and refining:

Figure 3A and Figure 3B are comparison diagrams of metallographic structure of Mg-5Sn-1.5Sr magnesium alloy without adding Ca and adding Ca and refining:

Figure 4A and Figure 4B are comparison diagrams of metallographic structure of Mg-4Sn-2Sr magnesium alloy without adding Ca and adding Ca.

Detailed ways

The technical solutions and effects of the present invention will be further elaborated below through four specific examples.

Example 1: Under the protection of flux or gas, the Mg-3Sn-2Sr magnesium alloy is melted according to the corresponding composition ratio, and then the temperature is raised to 720 °C, and the Mg-19wt.%Ca master alloy is added; the amount of Ca added accounts for 2% of the total weight of the charge The percentage is 0.20wt.%, adding method: bake the Mg-19wt.%Ca master alloy at 100-150°C for 15-30 minutes, then use a pressure ladle to quickly press it below the alloy liquid level for about 2 minutes, stir and heat up to 730°C, and then refined with C ₂ Cl ₆ refining agent for 5-10 minutes. After refining, stir the alloy melt and stand at 740°C for 12 minutes. After standing, remove the surface scum, and then cast.

Example 2: Under the protection of flux or gas, the Mg-5Sn-3Sr magnesium alloy is melted according to the corresponding composition ratio, and then the temperature is raised to 730 ° C, and the Mg-19wt.%Ca master alloy is added; the amount of Ca added accounts for 2% of the total weight of the charge The percentage is 0.25wt.%, adding method: bake the Mg-19wt.%Ca master alloy at 100-150℃ for 15-30 minutes, then use a pressure ladle to quickly press it below the alloy liquid level for about 3 minutes, stir and heat up to 740°C, then refining with C ₂ Cl ₆ refining agent for 5-10 minutes, after refining, stir the alloy melt and stand at 740°C for 10 minutes, remove the surface scum after standing, and then cast.

Example 3: Under the protection of flux or gas, the Mg-5Sn-1.5Sr magnesium alloy is melted according to the corresponding composition ratio, and then the temperature is raised to 740°C, and the Mg-19wt.%Ca master alloy is added; the amount of Ca added accounts for the total weight of the charge The percentage is 0.16wt.%, adding method: bake the Mg-19wt.%Ca master alloy at 100-150℃ for 15-30 minutes, then use a pressure ladle to quickly press it into the alloy liquid level for about 6 minutes, stir and heat up to 750°C, and then refined with C ₂ Cl ₆ refining agent for 5-10 minutes. After refining, stir the alloy melt and stand at 740°C for 15 minutes. After standing, remove the surface scum, and then cast.

Example 4: Under the protection of flux or gas, the Mg-4Sn-2Sr magnesium alloy is melted according to the corresponding composition ratio and the temperature is raised to 740 ° C, and the Mg-19wt.%Ca master alloy is added; the amount of Ca added accounts for 2% of the total weight of the charge The percentage is 0.10wt.%, adding method: bake the Mg-19wt.%Ca master alloy at 100-150°C for 15-30 minutes, then use a pressure ladle to quickly press it below the alloy liquid level for about 3 minutes, stir and heat up to 740°C, then refining with C ₂ Cl ₆ refining agent for 5-10 minutes, after refining, stir the alloy melt and stand at 740°C for 10 minutes, remove the surface scum after standing, and then cast.

Table 1 shows the composition and structure analysis and performance test results of the above four examples and the Mg-Sn-Sr magnesium alloy without Ca addition. From the comparative analysis results in Table 1, it can be seen that after adding a certain amount of Ca to the Mg-Sn-Sr series magnesium alloy, the average size of the SrMgSn phase in the alloy structure is significantly reduced. At the same time, the tensile properties and creep properties of the alloy are improved.

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Claims (2)

1. method that adds SrMgSn phase in the Ca refinement Mg-Sn-Sr magnesiumalloy is characterized in that: said method is to realize that through in the Mg-Sn-Sr magnesiumalloy, adding the Mg-Ca master alloy per-cent that the add-on of Ca accounts for the furnace charge gross weight is 0.1-0.25wt.%; Said method is under flux or gas shield, is warmed up to 720-740 ℃ after the Mg-Sn-Sr magnesiumalloy is melted by corresponding composition proportion, adds the Mg-19wt.%Ca master alloy; The per-cent that the Ca add-on accounts for the furnace charge gross weight is 0.1-0.25wt.%; Adding method: the Mg-19wt.%Ca master alloy was toasted 15-30 minute at 100-150 ℃; With pressing wooden dipper to be pressed into the following 2-6 of alloy liquid level minute rapidly, be warmed up to 730-750 ℃ after the stirring then, use C then ₂Cl ₆Refining agent refining treatment 5-10 minute, the refining back that finishes is stirred alloy melt and was left standstill 10-15 minute at 740 ℃, leaves standstill to drag for surface scum after finishing, and casts then.

2. the method that adds SrMgSn phase in the Ca refinement Mg-Sn-Sr magnesiumalloy according to claim 1; It is characterized in that: said method is under flux or gas shield; The Mg-Sn-Sr magnesiumalloy is warmed up to 740 ℃ after by the fusing of corresponding composition proportion, adds the Mg-19wt.%Ca master alloy, the per-cent that the Ca add-on accounts for the furnace charge gross weight is 0.1-0.25wt.%; Adding method: the Mg-19wt.%Ca master alloy was toasted 15-30 minute at 100-150 ℃; With pressing wooden dipper to be pressed into the alloy liquid level rapidly following 3 minutes, be warmed up to 740 ℃ after the stirring then, use C then ₂Cl ₆Refining agent refining treatment 5-10 minute, the refining back that finishes is stirred alloy melt and was left standstill 10 minutes at 740 ℃, leaves standstill to drag for surface scum after finishing, and casts then.

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