METHOD FOR PRODUCING NATIONAL-STANDARD MAGNESIUM ALLOY INGOTS ON THE BASIS OF MAGNESIUM ALLOY WASTE MATERIAL

Abstract

A method comprises: sorting and removing impurities from magnesium alloy waste material, and cleaning and drying said material, the cleaning comprising high-pressure rinsing, pickling, and water washing, performed in sequence; preheating the magnesium alloy waste material obtained in step a, and adding material, melting, refining, removing impurities, and alloying to obtain a magnesium alloy liquid; casting ingots from the magnesium alloy liquid obtained in step b, to obtain magnesium alloy ingots conforming to national standards. The method directly takes magnesium alloy waste material as a raw material to produce magnesium alloy ingots conforming to national standards; the addition of costly high-purity magnesium is unnecessary, and the number of castings in which the amount of harmful elements meets specifications accounts for 98% or more of the total number of castings; 2% slightly exceed specifications, which does not constitute a severe number of times specifications are exceeded.

Claims

1. A method for producing GB-standard magnesium alloy ingots from magnesium alloy waste material, comprising the following steps: Step a. sorting, removing impurities from, cleaning and drying the magnesium alloy waste material, wherein the cleaning involves high-pressure cleaning, pickling, and water rinse performed in sequence; Step b. preheating, melting, refining, removing impurities from, and alloying the magnesium alloy waste material obtained in Step a, so as to obtain magnesium alloy liquid; and Step c. casting ingots using the magnesium alloy liquid obtained in Step b, so as to obtain GB-standard magnesium alloy ingots.

2. The method of claim 1, wherein in Step a, the high-pressure cleaning is performed under a pressure of 5 to 20 MPa.

3. The method of claim 1, wherein Step a involves cutting, sorting and removing impurities from, high-pressure cleaning, pickling, water rinse and drying the magnesium alloy waste material, and is divided into the following steps: Step a1: cutting each large piece of the magnesium alloy waste material into plural small pieces of the magnesium alloy waste material; Step a2: sorting and removing impurities from the cut magnesium alloy waste material pieces, so as to screen out impurities that are difficult to separate from the magnesium alloy waste material; Step a3: high-pressure cleaning the magnesium alloy waste material that has been sorted and has impurities removed; Step a4: pickling the magnesium alloy waste material that has been high-pressure cleaned; Step a5: water rinsing the magnesium alloy waste material that has been pickled; and Step a6: drying the magnesium alloy waste material that has been water rinsed.

4. The method of claim 3, wherein material holding for the high-pressure cleaning is realized using a meshed drum.

5. The method of claim 1, wherein the high-pressure cleaning is a primary high-pressure cleaning, or wherein where the magnesium alloy waste material has its surface covered by greasiness or demolding agents, the high-pressure cleaning includes a primary high-pressure cleaning and a secondary high-pressure cleaning.

6. The method of claim 1, wherein a cleaning agent for the high-pressure cleaning is a degreasing agent.

7. The method of claim 1, wherein a cleaning liquid for the high-pressure cleaning is water and/or a cleaning agent.

8. The method of claim 7, wherein a cleaning liquid for the primary high-pressure cleaning is water.

9. The method of claim 7, wherein a cleaning duration for the primary high-pressure cleaning is 10 to 30 min.

10. The method of claim 7, wherein a cleaning liquid for the secondary high-pressure cleaning is an aqueous solution containing a cleaning agent.

11. The method of claim 7, wherein a cleaning liquid for the secondary high-pressure cleaning has a temperature of 40 to 70 C.

12. The method of claim 7, wherein a cleaning duration for the secondary high-pressure cleaning is 5 to 10 min.

13. The method of claim 3, wherein Step a4 involves: a pickling liquid for the pickling has a pH value of 1 to 3, and a pickling duration for the pickling is 30 to 90 s.

14. The method of claim 1, wherein Step b comprises preheating, melting, detecting harmful elements for, refining, alloying, skimming slag from and setting aside under a controlled temperature the magnesium alloy waste material obtained in Step a, and is divided into the following steps: Step b1: preheating the magnesium alloy waste material obtained in Step a; Step b2: heating and melting the magnesium alloy waste material obtained in Step b1; Step b3: detecting contents of harmful elements in the magnesium alloy liquid obtained in Step b2, and determining whether to prepare the GB-standard magnesium alloy ingots according to the contents; Step b4: refining the magnesium alloy liquid detected in Step b3 for preparing the GB-standard magnesium alloy ingots; Step b5: alloying the magnesium alloy liquid obtained in Step b4; Step b6: detecting contents of metal elements in the magnesium alloy liquid obtained in Step b5; Step b7: analyzing to determine whether the contents of the metal element other than iron as detected in Step b6 are conforming, and proceeding to the next step if yes or, if not, repeating Step b5 and Step b6 until they become conforming; Step b8: skimming slag from the magnesium alloy liquid that has been verified as being conforming in Step b7; Step b9: standing the magnesium alloy liquid obtained in Step b8 while controlling its temperature; and Step b10: detecting and analyzing whether a content of iron in the magnesium alloy liquid obtained in Step b9 is conforming, and entering Step c if yes.

15. The method of claim 14, wherein in Step b, the magnesium alloy liquid is refined again while alloyed.

16. The method of claim 14 wherein in Step b4 or b5, the refining agent is added in a small amount for multiple times, and a total adding amount thereof is 15 to 25 kg/t.

17. The method of claim 14, wherein a refining duration for Step b4 or b5 is 15 to 30 min.

18. The method of claim 14 wherein in Step b5, criteria for metal elements for alloying are: Mg: magnesium ingots of Grade 1 or better; Al: aluminum ingots of Grade 1 or better; Zn: zinc ingots of Grade 1 or better; Mn: one of high-purity AlMn alloy, metal manganese powder with its purity greater than 99.8%, and anhydrous manganese chloride with its purity greater than 99.8%; Be: high-purity AlBe alloy.

19. The method of claim 18, wherein the alloy elements are optionally added in an order of: Mn, Al and Zn, Mg, and last Be.

20. The method of claim 1, wherein Step c comprising the following steps: Step c1: preheating an ingot mold, and applying an even layer of demolding paint over an inner surface of the ingot mold; Step c2: preheating a casting pump and a casting pipeline; and Step c3: connecting the casting pump and the pipeline, starting a casting machine to perform casting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0102] The invention as well as a preferred mode of use, further objectives and advantages thereof will be best understood by reference to the following detailed description of illustrative, non-limiting embodiments.

[0103] In the following examples, the reagents used are all commercially available ones, unless otherwise specified, and are used according to their instructions or relevant standards. In addition, the flux(es) and refining agent(s) used in the following examples are products of Binhai Heng Wang Light Metal Flux Co., Ltd.

Example 1

[0104] The present example uses discarded magnesium alloy products imported by Hunan S.R.M. Technology CO., Ltd. from Sweden with a batch number of 2013-10-05-A as the feedstock for producing AZ91D magnesium alloy ingots. The batch of magnesium alloy waste material sums 5000 tons. Waste having its surface carrying greasiness and demolding agents takes about 10% of the entire batch. The producing steps are as follows:

[0105] (1) Cutting: cutting the magnesium alloy waste material using a metal crusher to waste pieces whose maximum dimension is 100 mm;

[0106] (2) Sorting and removing impurities: screen waste material containing inseparable screws, rubber or plastic, waste material with its surface covered by organic coating, and non-magnesium material out from the cut magnesium alloy waste material, and reserving the remaining magnesium alloy waste material for later use;

[0107] (3) Primary high-pressure cleaning: performing primary high-pressure cleaning on the magnesium alloy waste material that has been sorted and has impurities removed using a heavy-duty hot-water high-pressure cleaning machine modeled 895-1, wherein the cleaning liquid is water, the pressure is 10 MPa, and the cleaning duration is 20 min;

[0108] (4) Secondary high-pressure cleaning: performing secondary high-pressure cleaning on the magnesium alloy waste material that have received the primary high-pressure cleaning using the heavy-duty hot-water high-pressure cleaning machine modeled 895-1, wherein the cleaning liquid is aqueous solution containing an acid water-based metal degreasing agent, in which the aqueous solution prepared according to its formula has a pH value of 5.5, and for the cleaning, the aqueous solution temperature is 55 C., the pressure is 10 MPa, and the cleaning duration is 10 min;

[0109] (5) Pickling: placing the magnesium alloy waste material that has received the secondary high-pressure cleaning into dilute hydrochloric acid solution having a pH value of 1.0 for pickling, wherein the pickling duration is 40 s;

[0110] (6) Water rinsing: combining rinsing and spraying to remove acid liquid and impurities remained on the surface of the obtained magnesium alloy waste material;

[0111] (7) Drying: combining air blowing and hot air drying to remove water remained on the surface of the cleaned magnesium alloy waste material;

[0112] (8) Sorting again: sorting unclean waste material and non-magnesium material out of the dried waste material, thereby finalizing pretreatment for the magnesium alloy waste material;

[0113] (9) Preheating: placing the sorted, clean waste material into an oven, preheating it for 10 min to 130 C., and exhausting evaporated moisture through an air-extracting device;

[0114] (10) Heating and melting: adding the preheated magnesium alloy waste material in batches into a high-temperature smelting furnace, while gradually adding 8% of a flux for covering and extinguishing fire, wherein the furnace temperature is 850-950 C.;

[0115] (11) Refining: throwing a refining agent in batches evenly, performing mechanical agitation and air-blowing agitation while using the refining agent to cover and extinguish fire, wherein the refining duration is 20 min, and the refining temperature is 720 C.;

[0116] (12) Sampling and analyzing: subjecting the obtained magnesium alloy liquid to sampling (recorded as Sample #1) and spectral analysis, determining whether harmful elements (such as Si, Cu, Ni) exceed limits according to the analysis, and if the contents are seriously excessed, directly casting non-standard magnesium alloy ingots, or if the contents are slightly excessed, using pure magnesium dilution to reducing the exceeding elements to a conforming range, or if the contents are conforming, determining adding amounts of different elements (such as Al, Zn, Mn) for alloying according to the analysis, wherein the detected harmful elements and the adding amount of the other metal elements for the present example are shown in Table 1.1:

TABLE-US-00002 TABLE 1.1 Results of Spectral Detection for Sample #1 Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 6.89 0.345 0.187 0.039 0.007 0.0072 0.0005 0.0003 Residue

[0117] As shown clearly in Table 1.1, the harmful elements Si, Cu, and Ni are all in limits set forth in GB standards, and the material could be directly subjected to the subsequent alloying/refining operation. According to Table 1.1, the calculated adding amounts for the alloy elements Al, Zn, Mn, and Be are shown in Table 1.2:

TABLE-US-00003 TABLE 1.2 Required Adding amount of Alloy Elements for Alloying AlBe Containing Required Element Al Zn Mn 1.0% Beryllium Total adding 65.0 kg 9.5 kg 4.0 kg 4.5 kg amount Note: At sampling, the magnesium alloy liquid's weight is 2,950 kg.

[0118] (13) Alloying/Refining: according to Table 2, adding all the alloy materials in sequence, evenly adding 2% of a refining agent while melting the alloy materials, and performing mechanical agitation and gas-blowing agitation, covering and extinguishing fire with the refining agent while agitating, wherein the alloying/refining duration is 15 min, and the temperature is 740 C.;

[0119] (14) Sampling and analyzing: performing spectral sampling and analysis on the magnesium alloy liquid obtained in the previous step (recorded as Sample #2), and subjecting it to the subsequent processing if conforming, or performing alloying/refining again if the obtained magnesium alloy liquid is non-conforming. The results of the analysis are shown in Table 1.3:

TABLE-US-00004 TABLE 1.3 Results of Spectral Detection for Sample #2 Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 9.01 0.632 0.321 0.040 0.006 0.0073 0.0005 0.0014 Residue

[0120] As can be seen in Table 1.3, the magnesium alloy liquid has all the alloy elements other than Fe measured as conforming, thus needing not to be alloyed/refined again;

[0121] (15) Skimming slag: placing the fully preheated skimming ladle into the magnesium alloy liquid slowly, until it sunk to the bottom of the smelting furnace, and blowing up magnesium slag from the bottom using dry N.sub.2, wherein since magnesium slag is greater than magnesium alloy liquid in specific weight, magnesium slag would settle in the skimming ladle, thereby achieving slag skimming;

[0122] (16) Setting aside under controlled temperature: before setting aside, adding a proper amount of GB standards alloy ingots according to the magnesium liquid's temperature, cooling the magnesium liquid to 6405 C., then immediately heating it to 660 to 670 C., and setting the magnesium alloy liquid aside, wherein the duration for setting aside is more than 40 min;

[0123] (17) Sampling, analyzing and subsequent processing: sampling the settled magnesium alloy liquid (recorded as Sample #3) for analysis; if the magnesium alloy liquid conforms standard, directly using the settled magnesium alloy liquid for casting ingots according to actual production conditions, or transferring the settled magnesium alloy liquid to a temperature-holding furnace; if not conforming, adding a proper amount of alloy materials as needed, and then casting ingots or performing liquid transferring operation, wherein for liquid transferring, sulphur powder is used for fire-extinguishing of the magnesium alloy liquid remained in the smelting furnace, and the remaining magnesium alloy liquid is protected using a covering agent, while noble gas is used in the temperature-holding furnace for protection, wherein the results of detection and analysis are shown in Table 1.4:

TABLE-US-00005 TABLE 1.4 Results of Spectral Detection for Sample #3 Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 8.98 0.629 0.250 0.039 0.003 0.0070 0.0005 0.0012 Residue

[0124] As can be seen in Table 1.4, alloy elements measured in the magnesium alloy are all conforming to GB standards, and the subsequent liquid transferring and ingot casting operations could be performed;

[0125] (18) Pretreatment on ingot mold: preheating an ingot mold to 180 C., and applying a layer of demolding paint evenly to the ingot mold's inner surface;

[0126] (19) Pouring: preheating and connecting the casting pump and the casting pipeline, and starting the casting machine to perform casting; and

[0127] (20) Post-treatment: performing post-treatment such as burnishing, printing codes on and packing the casted magnesium alloy ingots.

[0128] As measured, the magnesium alloy ingots made in the present example are compositionally conforming to Chinese national standards, wherein chloride ion content is 0.0010%, and there is only little flux mixture. In addition, as measured form Sample #1, in the magnesium alloy liquid of the present example, harmful elements conforming casts take 98% in total casts, and slightly non-conforming casts take 2%, without any seriously non-conforming casts.

Example 2

[0129] The present example is different from Example 1 in the contents of harmful elements measured in Step 12 after refinement in Step 11. The results are shown in Table 2.1:

TABLE-US-00006 TABLE 2.1 Results of Spectral Analysis for Refined Magnesium Alloy Liquid Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 7.12 0.321 0.201 0.053 0.008 0.0079 0.0007 0.0003 Residue Note: At sampling, the magnesium alloy liquid's weight is 2,550 kg.

[0130] It is thus clear from Table 2.1 that the content of the harmful element Si is slightly excessed, and thus brings the need of adding pure magnesium to reduce silicon. As determined using calculation, the required adding amount of pure magnesium is 400 kg. After pure magnesium is added, the melt is agitated thoroughly before sampled again for harmful element analysis. The results are shown in Table 2.2:

TABLE-US-00007 TABLE 2.2 Results of Spectral Analysis of Magnesium Alloy Liquid after Addition of Pure Magnesium Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 6.21 0.280 0.178 0.046 0.008 0.0081 0.0008 0.0002 Residue

[0131] It is thus clear from Table 2.2 that the content of the harmful element Si is 0.046%, conforming to Chinese national standards, so the melt could be put into the subsequent alloying/refining operation directly.

[0132] Given the addition of pure magnesium, the amount of the alloy materials added for subsequent alloying is adjusted, but the rest part of the operation is identical to Example. The required adding amount of alloy elements for alloying is calculated according to Table 2.1 and 2.2. The results are shown in Table 2.3:

[0133] Table 2.3 Required Adding amount of Alloy Elements for Alloying:

TABLE-US-00008 TABLE 2.3 Required Adding amount of Alloy Elements for Alloying AlBe Containing Required Element Al Zn Mn 1.0% beryllium Total adding 84.0 kg 11.0 kg 5.0 kg 5.0 kg amount

[0134] The contents of alloy elements subsequently measured in the magnesium alloy liquid are shown in Table 2.4:

TABLE-US-00009 TABLE 2.4 Results of Spectral Detection for Sample #2 Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 8.96 0.638 0.310 0.045 0.006 0.0079 0.0007 0.0013 Residue

[0135] As can be seen in Table 2.4, the magnesium alloy liquid is conforming, with the contents of all the alloy elements other than Fe within the limits as set forth in GB standards, and thus it could receive the subsequent processing.

[0136] As measured, the magnesium alloy ingots made in the present example are compositionally conforming to Chinese national standards, wherein chloride ion content is 0.0010%, and there is only little flux mixture. In addition, as measured form Sample #2, in the magnesium alloy liquid of the present example, harmful elements conforming casts take 98% in total casts, and slightly non-conforming casts take 2%, without any seriously non-conforming casts.

Example 3

[0137] The present example is different from Example 1 in that its target magnesium alloy ingots are AM60B. Since the target magnesium alloy ingots are different, the alloy elements needed to be added are different.

[0138] According to results of the spectral analysis of Step 12, the subsequent operations are adjusted. Results of the spectral analysis are shown in Table 3.1

TABLE-US-00010 TABLE 3.1 Results of Spectral Analysis Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 6.98 0.332 0.198 0.038 0.008 0.0069 0.0007 0.0003 Residue Note: At sampling, the magnesium alloy liquid's weight is about 1,650 kg.

[0139] As can be seen in Table 3.1, among the main elements, the contents of aluminum and zinc content are excessed, with the content of zinc significantly exceeding the limit. This brings about the need of adding pure magnesium to reduce zinc and the need of supplementing aluminum, manganese and beryllium as well. As calculated, the type and weight of the elements added are shown in Table 3.2:

TABLE-US-00011 TABLE 3.2 Type and Weight of Elements Added for Alloying Added Pure Aluminum Manganese 1.0% Aluminum material Magnesium Ingots Powder Beryllium Alloy Adding 1300 60 7.0 5.0 amount (kg)

[0140] The element materials are added according to Table 3.2. After fully agitation, the magnesium alloy liquid is sampled again for spectral analysis. Results of the analysis are shown in Table 3.3:

TABLE-US-00012 TABLE 3.3 Results of Spectral Analysis after Elements Added Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 5.96 0.188 0.385 0.025 0.008 0.0075 0.0008 0.0015 Residue

[0141] As can be seen in Table 3.3, the magnesium alloy liquid is conforming, with the contents of all the alloy elements other than Fe within the limits as set forth in GB standards, and thus it could receive the subsequent processing.

[0142] As measured, the magnesium alloy ingots made in the present example are compositionally conforming to Chinese national standards, wherein chloride ion content is 0.0010%, and there is only little flux mixture. In addition, as measured form Sample #3, in the magnesium alloy liquid of the present example, harmful elements conforming casts take 98% in total casts, and slightly non-conforming casts take 2%, without any seriously non-conforming casts.

Comparative Example 1

[0143] The present comparative example is similar to Example 1 except that it eliminates the foregoing pretreatment. The magnesium alloy liquid obtained after the melting and refining steps is sampled for spectral analysis and the results are shown in the table below:

TABLE-US-00013 TABLE a Results of Spectral Analysis of Magnesium Alloy Liquid Obtained without Pretreatment Element Al Zn Mn Si Fe Cu Ni Be Mg Content (%) 7.56 0.452 0.286 0.326 0.025 0.152 0.052 0.0004 Residue

[0144] It is thus clear from Table a that harmful elements Si, Fe, Cu, and Ni are seriously excessed, so the material fails to meet the requirements for producing GB-standard magnesium alloy ingots in an industrialized process, and could be only used to produce non-standard magnesium alloy ingots.

Comparative Example 2

[0145] The traditional process is used to produce AZ91D magnesium alloy ingots same as those made in Example 1, and alloy materials added for alloying are shown in Table b below:

TABLE-US-00014 TABLE b Type and Weight of Elements Added for Alloying AlBe Containing Required Element Al Zn Mn 1.0% beryllium Total adding 270 kg 19.5 kg 9.0 kg 5.0 kg amount

[0146] As can be seen in Table b, using the traditional method to produce the magnesium alloy ingots as those produced in Example 1 requires pure magnesium as feedstock, and the required adding amounts of alloy elements are much higher than those for the present invention. It is thus clear that the method for producing magnesium alloy ingots as disclosed herein requires less input and lower costs and is favorable to material cycles, energy conservation and environmental protection.

[0147] From the aforementioned experimental results, it is clear that the disclosed method produces GB-standard magnesium alloy ingots by directly using magnesium alloy waste material as feedstock. The disclosed method features that GB-standard magnesium alloy ingots can be produced purely with discarded magnesium alloy products as its feedstock, without adding expensive high-purity magnesium. In production, conforming casts take 98% in total casts in terms of harmful element, and slightly non-conforming casts take 2%, without any seriously non-conforming casts. Additionally, as compared to the existing methods, the disclosed method is advantageous for needing less alloy elements addition, consuming much less energy, having higher use value, significantly reducing production costs, being easy to implement, involving simple operation, and being suitable for industrialization, and thus shows significant advancement.

[0148] The present invention has been described with reference to the preferred embodiments and it is understood that the embodiments are not intended to limit the scope of the present invention. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the concept of the present invention should be encompassed by the appended claims.