LU501002B1 - Method for optimizing microstructure and property of secondary aluminum - Google Patents

Abstract

Disclosed is a method for optimizing a microstructure and property of secondary aluminum, belonging to the field of metals.

Description

METHOD FOR OPTIMIZING MICROSTRUCTURE AND PROPERTY OF HUS01002

SECONDARY ALUMINUM TECHNICAL FIELD

[01] The present disclosure relates to the field of metals, and in particular relates to a method for optimizing a microstructure and property of secondary aluminum.

BACKGROUND ART

[02] Raw materials of recycled aluminum come from scrap aluminum alloy. Due to irregular recycling of scrap aluminum and backward technology in China, a composition of recycled aluminum is very complicated, which limits use of the recycled aluminum.

SUMMARY

[03] The present disclosure is implemented as follows:

[04] A method for optimizing a microstructure and property of secondary aluminum, includes: with rare earth yttrium or rare earth gadolinium as a modifier, smelting an aluminum alloy with the modifier.

[05] A modified alloy is prepared according to the method for optimizing a microstructure and property of secondary aluminum.

[06] Beneficial effects:

[07] The method for optimizing a microstructure and property of secondary aluminum provided by the present disclosure uses the rare earth yttrium as a modifier. When the alloy is smelted, yttrium can bond with specific elements in the alloy, so that the specific elements are consumed, and in turn, the microstructure is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[08] FIG. 1 shows a metallographic microstructure of a secondary alloy aluminum-alloy die casting (ADC) 12.

[09] FIG. 2 shows an X-ray diffraction (XRD) pattern of a modified alloy obtained by adding

1.2 wt% rare earth yttrium to the secondary alloy ADC12.

[10] FIG. 3 shows an energy dispersion spectrum (EDS) pattern of the secondary alloy ADC12.

[11] FIG. 4 shows a microstructure of an impurity iron phase after different amounts of rare earth yttrium is added to the secondary alloy ADC12.

[12] FIG. 5 shows EDS patterns of the secondary alloy ADC12 to which different amounts of 1 rare earth yttrium is added. 7501002

[13] FIG. 6 shows mechanical properties of the secondary alloy ADC12 to which different amounts of rare earth yttrium is added.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[14] The present disclosure provides a method for optimizing a microstructure and property of secondary aluminum. A modification method includes: with rare earth yttrium or rare earth gadolinium as a modifier, smelting an alloy with the modifier.

[15] The modification as described in the present disclosure may include: adding some substances to metal (such as alloy) liquid to disperse the substances in the metal, and conducting smelting to improve and enhance the material properties.

[16] The rare earth yttrium may be a metal element or alloy of yttrium, and the rare earth gadolinium may be a metal element or alloy of gadolinium.

[17] Introduction of the rare earth yttrium and rare earth gadolinium can remove impurities from the alloy and improve the microstructure and mechanical properties of the alloy. By introducing the rare earth yttrium and rare earth gadolinium, primary a-Al grains and modified eutectic silicon can be refined. The rare earth yttrium and rare earth gadolinium can promote increase in the tensile property of an aluminum alloy, improve the electrical conductivity and resistance to recrystallization of an Al-Zr alloy, and enhance the thermal stability of an Al-Mg-Si alloy.

[18] Addition of the rare earth yttrium and rare earth gadolinium to the aluminum alloy has a positive effect on refinement and homogenization of an iron-rich phase.

[19] The alloys as described in the present disclosure may be secondary alloys or other alloys. Some optional examples of secondary aluminum alloys are ADC6 and ADC12. In terms of mass fraction, the chemical composition of the ADC12 aluminum alloy is as follows: 12.0% Si, 1.51% Cu, 0.81% Fe, 0.96% Zn, 0.23% magnesium, 0.22% manganese, 0.19-2.0% Gr, 0.19% Ni, and the balance of Al.

[20] Charge of a certain proportion is put into a smelting furnace and heated to melt to obtain melt. The composition of the melt is adjusted to obtain alloy liquid which meets the requirements. In the smelting process, corresponding measures are taken to control the content of gas and oxide inclusions, so that the content of each component or impurity element in the melt meets the specified composition, ensuring that alloy liquid of a proper microstructure and high quality is obtained for a casting.

[21] An example of the method for optimizing a microstructure and property of secondary aluminum includes: 2

[22] (1) Pretreatment of scrap aluminum: 1001008

[23] Recycled scrap aluminum is primarily classified and stacked in grades. Scrap aluminum products should be disassembled, and steel and other non-ferrous metal parts connected with the aluminum should be separated. Then the scrap aluminum is subjected to washing, crushing, magnetic separation, organic substance removal, screening, drying and other processes. According to the weight of smelting molten aluminum and the percentage content of the composition of a secondary aluminum alloy, some specific recycled scrap aluminum with relatively stable composition and similar composition content are selected, and the amount of various scraps is calculated.

[24] (2) Smelting equipment preparation:

[25] The experiment uses an intermediate frequency induction smelting furnace. In order to ensure the quality of aluminum alloy ingots and extend the service life of the smelting furnace as much as possible, the smelting furnace must be cleaned and washed in advance. A graphite crucible is used as a smelting vessel, and the crucible is placed in a designated position in the smelting furnace. After smelting, a steel mold is used for casting. Before smelting, the inner surface of a metal mold is polished with sandpaper to remove remaining metal, oxide skin and other sundries. In order to ensure that the castings are easy to demold, a thin layer of boron nitride is applied to the inner surface of the steel mold. The prepared steel mold is placed on a tray in the furnace to ensure that melt can be poured into the mold smoothly.

[26] (3) Loading secondary aluminum:

[27] During smelting, the order and method of loading the charge not only affect the smelting time, melting loss of metal and heat consumption, but also affect the quality of alloy melt and the service life of the furnace. Therefore, the order of loading the charge should be appropriate and reasonable. During furnace loading, first small or thin scraps are loaded, aluminum ingots and large pieces are loaded in the middle, and finally rare earth yttrium is loaded. To prevent the rare earth yttrium from sinking directly to the bottom of the crucible, the rare earth yttrium is wrapped with polished aluminum foil and then placed in the middle of the crucible.

[28] The crucible is preferably a graphite crucible, that is, both the rare earth yttrium and the charge (aluminum alloy scraps) are placed in the graphite crucible. Before loading the rare earth yttrium into the charge, preferably the charge is melted into liquid to form charge melt, and then the rare earth yttrium is wrapped with aluminum foil and put into the melt.

[29] (4) Vacuum treatment: A furnace door and an intake valve are closed, a cooling water valve and an exhaust valve are opened, a power switch is turned on, and then a mechanical pump is turned on for vacuumizing. When the pressure is 10“ Pa, the exhaust valve is closed and the intake valve is opened. After argon is into the smelting furnace to about 0.75 MPa, the intake 3 valve is closed, and the above operations are repeated three times to remove oxygen from the 501002 furnace by vacuum treatment, thereby preventing aluminum melting loss in the smelting process which reduces the recovery rate of the scrap aluminum.

[30] The vacuum treatment can remove oxidizing gas (e.g. oxygen) from the smelting furnace, thereby suppressing the oxidizing atmosphere in the smelting furnace, and replacing it with a non-oxidizing atmosphere (e.g. argon).

[31] (5) Heating to melt: After being loaded, the charge can be heated to melt. During melting, first a heating switch is turned on, the temperature is slowly adjusted to 300°C, and the scrap aluminum, the crucible and other devices are preheated for 20 min. Then the temperature is adjusted to 750°C to start heating and melting. Melting is the process of transformation from solid to liquid. The quality of this process has a decisive influence on the quality of a product. During melting, care should be taken to prevent the melt from overheating. After the charge is melted, the melt should be properly stirred.

[32] (6) Stirring: After the melt is completely melted, the temperature of the melt is adjusted to 720°C for overheating for 1 hour, and the melt should be stirred. The purpose of stirring is to not only make the temperature uniform everywhere in the melt and prevent local overheating of the melt, but also accelerate dissolution of the rare earth yttrium, so that the alloy composition is evenly distributed. An electromagnetic stirring system of the smelting furnace can realize non-contact stirring of the melt, will not cause new contamination to the melt in the stirring process or change the alloy composition of the melt, and is beneficial to control the iron content. Because an element with a higher density is likely to sink to the bottom, and the addition of the rare earth yttrium cannot be absolutely uniform, if the stirring is not thorough, it is easy to cause unevenness of the chemical composition of the melt. As the amount of the rare earth yttrium added increases, the frequency of stirring should be increased to ensure that the melt is stirred every 10 min. The stirring should be conducted steadily, without causing too much waves to prevent the molten aluminum from splashing out.

[33] When mechanical equipment is used for stirring, a stirring rod is preferably a graphite rod.

[34] (7) Pouring: After heat preservation, the melt should be poured as soon as possible to avoid lowering of the melt temperature. During pouring, the speed should be slightly low at the very start to prevent molten metal from overflowing a sprue cup and severely impacting a cavity. Then, the pouring speed should be increased to fill the sprue cup while keeping stable without interrupting the flow. The pouring process should has no cold shut and smooth exhaust without damaging a core.

[35] (8) Mold unloading: After pouring, power is turned off to cool in the furnace. Then the 4 furnace door is opened, the steel mold is taken out for demolding, and the casting is taken out re 501002 observe whether the casting is qualified. If the casting has defects, measures should be taken to solve the defects until the casting is qualified.

[36] The present disclosure further provides a secondary alloy, which is prepared according to the aforementioned method for optimizing a microstructure and property of secondary aluminum.

[37] Example 1

[38] A modified alloy was obtained by modifying an ADC12 aluminum alloy ( secondary aluminum alloy). ADC12, also known as No. 12 aluminum, is a Japanese brand, which is an Al-Si-Cu series alloy and a die-cast aluminum alloy.

[39] A method for preparing the modified alloy is as follows:

[40] The smelting equipment was an intermediate frequency induction smelting furnace.

[41] In the smelting furnace, a secondary aluminum alloy was put into a graphite crucible and heated to 740°C. After the aluminum alloy was completely melted, the aluminum melt was slagged off. Then the temperature was increased to 760°C, and different contents of rare earth yttrium was wrapped with aluminum foil. The contents (mass fractions) of the rare earth yttrium were 0 (reference example), 0.2%, 0.5%, 1.2%, and 2.0% respectively, and the rare earth yttrium was pressed into the melt using a bell jar. Then the melt was stirred evenly with a graphite rod, subjected to heat preservation for 20 min and then cooled in the furnace to obtain products numbered I, II, II, IV, and V.

[42] Test Example 1

[43] The products I, II, III, IV, and V prepared in Example 1 were respectively poured to obtain castings, and samples with a size of 12x12x12 mm were cut off respectively, and marked as products I-1, II-1, III-1, IV-1, and V-1.

[44] The products I-1, II-1, III-1, IV-1, and V-1 were sanded, mechanically polished, etched with a 0.5% hydrogen fluoride (HF) aqueous solution, scrubbed with alcohol and dried to obtain metallographic samples JX-1, JX-2, JX-3, JX-4, and JX-5.

[45] The metallographic microstructure and morphology of the samples were observed under an Axiovert 40MAT optical microscope. The microstructure and composition of the alloys were observed and analyzed using a scanning electron microscope (SEM) with an energy spectrometer. The phase composition of the alloys was analyzed using a Bruker D-8 X-ray diffractometer. The mechanical properties of the materials were measured on a WDW-100KN electronic universal testing machine, and the tensile speed was 0.2 mm/min. Three samples were taken respectively for the alloys with different yttrium contents for the test, and the average value was finally taken.

[46] Analysis of test and results:

[47] From FIGs. 1-3, the solidified microstructures of the ADC12 alloy are mainly a-Al 0% (marked as A in FIG. 1) and Al-Si eutectic structures (marked as B in FIG. 1). Other impurities are mainly Cu, Zn, and Fe. The impurity Cu mainly exists in the form of Al2Cu, the impurity Zn is randomly and uniformly distributed on an a-Al matrix, and Fe is mainly present in the a-Al matrix in the form of B-Fe (AISFeSi) phase (marked as C in FIG. 1).

[48] Influence of rare earth yttrium on B-Fe phase:

[49] The elongated area marked as C in FIG. 1 is an acicular iron-rich phase. X-ray diffraction analysis showed that the phase composition of the iron-rich phase is mainly AISFeSi. In the solidification process of an alloy, due to low solubility of iron, it is easy to form intermetallic compounds with other elements at grain boundaries and precipitate.

[50] After different contents of rare earth yttrium was added to the ADC12 aluminum alloy, the change in the impurity iron phase is shown in FIG. 4. Compared with the iron-rich phase without rare earth yttrium (0 wt% Y) added, it can be seen that the size of the iron-rich phase with the rare earth yttrium added is significantly smaller. With the increase in the yttrium content, the B-Fe phase gradually becomes shorter, and is distributed gradually from aggregation to dispersion. When the addition amount of the rare earth yttrium is 1.2%, the B-Fe phase is in the shape of short rods and is evenly distributed in the matrix. When the yttrium content exceeds

1.2%, B-Fe becomes coarse on the contrary and also aggregates to a certain extent. [S1] In addition, relatively bright new precipitates were formed near the P-Fe phase. The sample with the 1.2% yttrium addition amount was subjected to XRD analysis (FIG. 2, curve b), and the new intermetallic compound formed was determined as Al2Si2Y by XRD analysis, which might be because yttrium had a larger atomic number, the Al12Si2Y phase was brighter. The bright spot is subjected to energy spectrum analysis, and the results are shown in FIG. 5. The percentage content of each component showed that the intermetallic compound was Al2Si2Y, which proved the above conclusion. [S2] The modification mechanism of the rare earth yttrium on the B-Fe phase is mainly as follows: [S3] 1) As shown in FIG. 2 and FIG. 5, the added rare earth yttrium could react with Al and Si in the aluminum melt to form a new precipitated phase Al2Si2Y, which consumed Si in the aluminum alloy, thereby effectively reducing the formation of a B-Fe (AISFeSi) phase.

[54] 2) From FIG. 4, the formed Al2Si2Y phase adsorbed around the B-Fe phase, and the growth direction of the B-Fe phase was restricted, thereby preventing the growth of the P-Fe phase. [S5] 3) The intermetallic compound formed by the rare earth yttrium mainly accumulated at the grain boundaries. These fine AI2S12Y phases played a role in heterogeneous nucleation and 6 increased the nucleation rate of the ß-Fe phase. From FIG. 4, when the amount of rare carth 998 yttrium added exceeded 1.2%, the B-Fe phase became coarse on the contrary, mainly because excessive addition of the yttrium forms a large amount of intermetallic compounds. These intermetallic compounds were pushed to grain boundaries with dendritic growth, and then aggregated and grew to coarsen. The dispersed fine Al2Si2Y phases were reduced, resulting in a reduction in B-Fe phase nucleation, and the B-Fe phase became coarser. After the rare earth phase coarsened, the adsorption on the surface of the P-Fe phase weakened, which reduced the inhibitory effect on the B-Fe phase, and the B-Fe phase could grow more freely. [S6] Influence of rare earth yttrium on mechanical properties of ADC12 alloy: [S7] From FIG. 6, compared with no addition of rare earth yttrium, the mechanical properties of the alloy after the addition of yttrium were significantly improved. With the addition of rare earth yttrium, the tensile strength and elongation of the ADC12 aluminum alloy increased to a certain extent. When the mass fraction of yttrium was 1.2%, the mechanical properties of the ADC12 were optimal. At this time, the tensile strength was 139.66 MPa, and the elongation was

3.56%, which were 36.58% and 51.24% higher than those of the alloy not modified by yttrium respectively. This is because after the addition of yttrium, the intermetallic compound AI2S12Y was formed and refined the B-Fe phase. Yttrium is an excellent modifier, which can effectively refine the primary a-Al and eutectic silicon, and reduce a separating effect on a matrix, so the mechanical properties are improved. When the yttrium content increased to 2.0%, the mechanical properties of the alloy began to decrease, because as the yttrium content increased, a larger amount of AI2Si2Y phases were formed. Moreover, these intermetallic compounds gradually grew up and presented a coarse and long morphology, which not only caused stress concentration, but also weakened the refinement effect, which coarsened the ß-Fe phase to a certain extent, so that the mechanical properties were reduced. The size, morphology and content of a-Al dendrites, eutectic silicon and intermetallic compounds will affect the mechanical properties of alloys. When the content of rare earth yttrium exceeded 0.3%, due to massive formation of the AI2Si2Y phase and coarsening of the a-Al dendrites, the eutectic silicon and the B-Fe phase, the mechanical properties of a secondary Al-0.7Si-0.3Mg-1.0Fe alloy decreased. [S8] Addition of the rare earth Y to the secondary ADC12 aluminum alloy could form a new intermetallic compound AlI2Si2Y phase, which had a significant modification effect on the B-Fe phase. When the content of rare earth yttrium was 1.2%, the B-Fe phase changed from the original acicular shape to the short rod shape, and was uniformly distributed at the grain boundaries. The Al2Si2Y phase could significantly improve the mechanical properties of the secondary ADC12 aluminum alloy. When the mass fraction of rare earth yttrium was 1.2%, the mechanical properties of the ADC12 were optimal. The tensile strength and elongation at this 7 time were 139.6 MPa and 3.56% respectively, which were 36.58% and 51.24% higher than those of the alloy without rare earth yttrium added. 8

Claims (7)

WHAT IS CLAIMED IS:

1. A method for optimizing a microstructure and property of secondary aluminum, comprising: with rare earth yttrium or rare earth gadolinium as a modifier, smelting an aluminum alloy with the modifier.

2. The method for optimizing a microstructure and property of secondary aluminum according to claim 1, wherein when the alloy and the modifier are smelted, the alloy and the modifier are both placed in a vessel made of graphite.

3. The method for optimizing a microstructure and property of secondary aluminum according to claim 1, wherein a method for smelting the alloy and the modifier comprises: melting the alloy into melt, then placing the modifier in the melt for smelting, and stirring with a graphite rod.

4. The method for optimizing a microstructure and property of secondary aluminum according to claim 1, wherein the smelting of the alloy and the modifier is conducted in a non-oxidizing atmosphere, the non-oxidizing atmosphere is an argon atmosphere with a pressure of 0.75 MPa.

5. The method for optimizing a microstructure and property of secondary aluminum according to any one of claims 1-4, wherein a model of the aluminum alloy comprises alloy aluminum-alloy die castings (ADC) 12 and ADC6, and a chemical composition of the ADC12 aluminum alloy in mass fraction is as follows: 12.0% Si, 1.51% Cu, 0.81% Fe, 0.96% Zn, 0.23% magnesium, 0.22% manganese, 0.19-2.0% Gr, 0.19% Ni, and the balance of Al.

6. The method for optimizing a microstructure and property of secondary aluminum according to claim 5, wherein the aluminum alloy is ADC12, and a method for smelting the aluminum alloy and the modifier comprises: putting the aluminum alloy in a graphite crucible for preheating treatment, then continuing heating until the aluminum alloy melts into a liquid aluminum alloy, at the same time, placing rare earth yttrium or rare earth gadolinium in the liquid aluminum alloy, and conducting heat preservation and cooling while stirring.

7. A modified alloy, prepared by the method for optimizing a microstructure and property of 9

. . . LU501002 secondary aluminum according to any one of claims 1-6.