Patent Application
20120037332
The present invention relates to the use of Al-based intermediate alloy in processing, especially the use of aluminum-zirconium-titanium-carbon intermediate alloy in wrought processing of magnesium and magnesium alloy.
The use of magnesium and magnesium alloys in industries started in 1930's. Since magnesium and magnesium alloys are the lightest structural metallic materials at present, and have the advantages of low density, high specific strength and stiffness, good damping shock absorption, heat conductivity, and electromagnetic shielding performance, excellent machinability, stable part size, easy recovery, and the like, magnesium and magnesium alloys, especially wrought magnesium alloys, possess extremely enormous utilization potential in the filed of transportation, engineering structural materials, and electronics. Wrought magnesium alloy refers to the magnesium alloy which can be formed by plastic molding methods such as extruding, rolling, forging, and the like. However, due to the constraints in, for example, material preparation, processing techniques, anti-corrosion performance and cost, the use of magnesium alloy, especially wrought magnesium alloy, is far behind steel and aluminum alloys in terms of utilization amount, resulting in a tremendous difference between the developing potential and practical application thereof, which never occurs in any other metal materials.
The difference of magnesium from other commonly used metals such as iron, copper, and aluminum lies in that, its alloy exhibits closed-packed hexagonal crystal structure, has only 3 independent slip systems at room temperature, is poor in plastic wrought, and is significantly affected in terms of mechanical property by grain sizes. Magnesium alloy has relatively wide range of crystallization temperature, relatively low heat conductivity, relatively large volume contraction, serious tendency to grain growth coarsening, and defects of generating shrinkage porosity, heat cracking, and the like during setting. Since finer grain size facilitates reducing shrinkage porosity, decreasing the size of the second phase, and reducing defects in forging, the refining of magnesium alloy grains can shorten the diffusion distance required by the solid solution of short grain boundary phases, and in turn improves the efficiency of heat treatment. Additionally, finer grain size contributes to improving the anti-corrosion performance and machinability of the magnesium alloys. The application of grain refiner in refining magnesium alloy melts is an important means for improving the comprehensive performances and forming properties of magnesium alloys. The refining of grain size can not only improve the strength of magnesium alloys, but also the plasticity and toughness thereof, thereby enabling large-scale plastic processing and low-cost industrialization of magnesium alloy materials.
It was found in 1937 that the element that has significantly refining effect for pure magnesium grain size is Zr. Studies have shown that Zr can effectively inhibits the growth of magnesium alloy grains, so as to refine the grain size. Zr can be used in pure Mg, Mg—Zn-based alloys, and Mg—RE-based alloys, but can not be used in Mg—Al-based alloys and Mg—Mn-based alloys, since it has a very small solubility in liquid magnesium, that is, only 0.6 wt % Zr dissolved in liquid magnesium during peritectic reaction, and will be precipitated by forming stable compounds with Al and Mn. Mg—Al-based alloys are the most popular, commercially available magnesium alloys, but have the disadvantages of relatively coarse cast grains, and even coarse columnar crystals and fan-shaped crystals, resulting in difficulties in wrought processing of ingots, tendency to cracking, low finished product rate, poor mechanical property, and very low plastic wrought rate, which adversely affects the industrial production thereof. Therefore, the problem existed in refining magnesium alloy cast grains should be firstly addressed in order to achieve large-scale production. The methods for refining the grains of Mg—Al-based alloys mainly comprise overheating method, rare earth element addition method, and carbon inoculation method. The overheating method is effective to some extent; however, the melt is seriously oxidized. The rare earth element addition method has neither stable nor ideal effect. The carbon inoculation method has the advantages of broad source of raw materials and low operating temperature, and has become the main grain refining method for Mg—Al-based alloys. Conventional carbon inoculation methods add MgCO3, C2Cl6, or the like to a melt to form large amount of disperse Al4C3 mass points therein, which are good heterogeneous crystal nucleus for refining the grain size of magnesium alloys. However, such refiners are seldom adopted because their addition often causes the melt to be boiled. In summary, a general-purpose grain intermediate alloy has not been found in the industry of magnesium alloys, and the applicable range of various grain refining methods depends on the alloys or the components thereof. Therefore, one of the keys to achieve the industrialization of magnesium alloys is to find a general-purpose grain refiner capable of effectively refining cast grains when solidifying magnesium and magnesium alloys and a method using the same in continuous production.
The use of aluminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy in the wrought processing of magnesium and magnesium alloys is provided in order to address the above-mentioned problems existing at present.
The present invention adopts the following technical solution: the use of aluminum-zirconium-titanium-carbon intermediate alloy in wrought processing of magnesium and magnesium alloys, wherein the aluminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy has a chemical composition of: 0.01% to 10% Zr, 0.01% to 10% Ti, 0.01% to 0.3% C, and Al in balance, based on weight percentage; the wrought processing is plastic molding; and the use is to refine the grains of magnesium or magnesium alloys.
Preferably, the aluminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy has a chemical composition of: 0.1% to 10% Zr, 0.1% to 10% Ti, 0.01% to 0.3% C, and Al in balance, based on weight percentage. More preferably, the chemical composition is: 1% to 5% Zr, 1% to 5% Ti, 0.1% to 0.3% C, and Al in balance.
Preferably, the content of impurities present in the aluminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy are: Fe of no more than 0.5%, Si of no more than 0.3%, Cu of no more than 0.2%, Cr of no more than 0.2%, and other single impurity element of no more than 0.2%, based on weight percentage.
Preferably, the plastic molding is performed by extruding, rolling, forging or the combination thereof. When the plastic molding is performed by rolling, casting and rolling is preferably adopted to form plate or wire materials. The casting and rolling process comprises sequentially and continuously performing the steps of melting, temperature-adjusting, and casting and rolling magnesium or magnesium alloys. More preferably, the aluminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy is added to the melt of magnesium or magnesium alloys after the temperature adjusting step and before the casting and rolling step. Still more preferably, the temperature adjusting step adopts a resistance furnace, the casting and rolling step adopts casting roller, the resistance furnace is provided with a liquid outlet at the lower end of the side wall, the casting rollers are provided with an engaging zone, a melt delivery pipe is connected between the liquid outlet and the engaging zone, and the aluminum-zirconium-titanium-carbon intermediate alloy is added to the melt of magnesium or magnesium alloy via the grain refiner inlet. Most preferably, the grain refiner inlet is provided with an agitator which uniformly disperses the aluminum-zirconium-titanium-carbon intermediate alloy in the melt of magnesium or magnesium alloy by agitating. Further preferably, the space over the melt of magnesium or magnesium alloy in the grain refiner inlet is filled with protective gas, which is a mixture gas of SF6 and CO2.
More preferably, the aluminum-zirconium-titanium-carbon intermediate alloy is a wire having a diameter of 9 to 10 mm.
The present invention has the following technical effects: providing an aluminum-zirconium-carbon (Al—Zr—Ti—C) intermediate alloy and the use thereof in the plastic wrought processing of magnesium or magnesium alloys as a grain refiner, which has the advantages of great ability in nucleation and good grain refining effect; and further proving a method for using the aluminum-zirconium-titanium-carbon intermediate alloy in casting and rolling magnesium and magnesium alloys, which can achieve continuous and large-scale production of wrought magnesium and magnesium alloy materials.
The present invention can be further expressly explained by specific examples of the invention given below which, however, are not intended to limit the scope of the present invention.
Commercially pure aluminum, zirconium scarp, titanium sponge and graphite powder were weighed in a weight ratio of 94.85% Al, 3% Zr, 2% Ti, and 0.15% C. The graphite powder had an average particle size of 0.27 mm to 0.83 mm. The graphite powder was soaked in 2 g/L KF aqueous solution at 65±3° C. for 24 hours, filtrated to remove the solution, dried at 120±5° C. for 20 hours, and then cooled to room temperature for use. Aluminum ingots were added to an induction furnace, melt, and heated to a temperature of 770±10° C., in which the zirconium scarp, the titanium sponge and the soaked graphite powder were sequentially added and completely dissolved under agitation. The resultant mixture was kept at the temperature, continuously and mechanically agitated to be homogenized, and then processed by casting and rolling into coiled wires of aluminum-zirconium-titanium-carbon intermediate alloy having a diameter of 9.5 mm.
Commercially pure aluminum, zirconium scarp, titanium scarp and graphite powder were weighed in a weight ratio of 83.8% Al, 9.7% Zr, 6.2% Ti, and 0.3% C. The graphite powder had an average particle size of 0.27 mm to 0.83 mm. The graphite powder was soaked in 4 g/L KF aqueous solution at 95±3° C. for 48 hours, filtrated to remove the solution, dried at 160±5° C. for 20 hours, and then cooled to room temperature for use. Aluminum ingots were added to an induction furnace, melt, and heated to a temperature of 720±10° C., in which the zirconium scarp, the titanium scarp and the soaked graphite powder were sequentially added and completely dissolved under agitation. The resultant mixture was kept at the temperature, continuously and mechanically agitated to be homogenized, and then processed by casting and rolling into coiled wires of aluminum-zirconium-titanium-carbon intermediate alloy having a diameter of 9.5 mm.
Commercially pure aluminum, zirconium scarp, titanium scarp and graphite powder were weighed in a weight ratio of 99.57% Al, 0.1% Zr, 0.3% Zr, and 0.03% C. The graphite powder had an average particle size of 0.27 mm to 0.55 mm. The graphite powder was soaked in a mixture aqueous solution of 1.2 g/L K2TiF6 and 0.5 g/L KF at 87±3° C. for 36 hours, filtrated to remove the solution, dried at 110±5° C. for 20 hours, and then cooled to room temperature for use. Aluminum was added to an induction furnace, melt, and heated to a temperature of 810±10° C. , in which the zirconium scarp, the titanium scarp and the soaked graphite powder were sequentially added and completely dissolved under agitation. The resultant mixture was kept at the temperature, continuously and mechanically agitated to be homogenized, and then processed by casting and rolling into coiled wires of aluminum-zirconium-titanium-carbon intermediate alloy having a diameter of 9.5 mm.
Pure magnesium was melt in an induction furnace under the protection of a mixture gas of SF6 and CO2, and heated to a temperature of 710° C., to which 1% Al—Zr—Ti—C intermediate alloy prepared according to examples 1-3 were respectively added to perform grain refining. The resultant mixture was kept at the temperature under mechanical agitation for 30 minutes, and directly cast into ingots to provide 3 groups of magnesium alloy sample subjected to grain refining.
The grain size of the samples were evaluated under GB/T 6394-2002 for the circular range defined by a radius of ½to ¾ from the center of the samples. Two fields of view were defined in each of the four quadrants over the circular range, that is, 8 in total, and the grain size was calculated by cut-off point method.
The pure magnesium without grain refining exhibited columnar grains having a width of 300 μm˜2000 μm and in scattering state. The 3 groups of magnesium alloys subjected to grain refining exhibited equiaxed grains with a width of 50 μm˜200 μm.
The results of the tests show that the Al—Zr—Ti—C intermediate alloys according to the present invention have very good effect in refining the grains of pure magnesium.
Reference is made to
| Number | Date | Country | Kind |
|---|---|---|---|
| 201110155839.9 | Jun 2011 | CN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CN11/77260 | 7/18/2011 | WO | 00 | 9/2/2011 |
