METHOD OF RECYCLING MIXED ALLOY SCRAP PARTS

Abstract

A method of processing mixed-material vehicle scrap includes conditioning the mixed-material vehicle scrap and heating the mixed-material vehicle scrap. The mixed-material vehicle scrap comprises a first group of parts and a second group of parts. The first group of parts includes a first alloy and the second group of parts has a substrate of a second alloy and a coating disposed over the substrate. The mixed-material vehicle scrap is conditioned such that an element of the second alloy is diffused into the coating to form a diffused coating. The diffused coating has a melting temperature greater than a melting temperature of the first alloy. The mixed-material vehicle scrap is heated to a temperature above the melting temperature of the first alloy and below the melting temperature of the diffused coating, thereby allowing the second group of parts to separate from the first group of parts.

Claims

1. A method of processing mixed-material vehicle scrap, the mixed-material vehicle scrap comprising a first group of parts and a second group of parts, the first group of parts comprising a first alloy and the second group of parts comprising a second alloy, each of the second plurality of parts having a substrate comprising the second alloy and a coating disposed over the substrate, the method comprising: conditioning the mixed-material vehicle scrap such that an element of the second alloy is diffused into the coating to form a diffused coating, the diffused coating having a melting temperature greater than a melting temperature of the first alloy; and heating the mixed-material vehicle scrap to a temperature above the melting temperature of the first alloy and below the melting temperature of the diffused coating, thereby allowing the second group of parts to separate from the first group of parts.

2. The method of claim 1, wherein the first alloy comprises an aluminum alloy.

3. The method of claim 1, wherein the first alloy comprises a magnesium alloy.

4. The method of claim 1, wherein the coating is applied with an electrocoating process.

5. The method of claim 1, wherein the coating comprises a zinc alloy.

6. The method of claim 1, wherein the coating has a thickness between about 2 microns and 10 microns.

7. The method of claim 1, wherein the diffused coating comprises gamma phase constituents.

8. The method of claim 1, wherein conditioning the mixed-material vehicle scrap comprises heating the mixed-material vehicle scrap to a temperature between about 450 C. and about 600 C. for up to about 60 minutes.

9. A method of processing mixed-material vehicle scrap, the mixed-material vehicle scrap comprising aluminum parts and steel parts, each of the steel parts comprising a steel substrate and a coating disposed over the steel substrate, the method comprising: conditioning the mixed-material vehicle scrap such that iron from each of the steel parts is diffused into each of the coatings to form a diffusion layer, the diffusion layer having a melting temperature greater than a melting temperature of the aluminum alloy; and heating the mixed-material vehicle scrap to a temperature above the melting temperature of the aluminum alloy and below the melting temperature of the diffusion layer, thereby allowing the steel parts to separate from the aluminum parts.

10. The method of claim 9, wherein the coating is applied with an electrocoating process.

11. The method of claim 9, wherein the coating comprises a zinc alloy.

12. The method of claim 9, wherein the coating has a thickness between about 2 microns and 10 microns.

13. The method of claim 9, wherein the diffusion layer comprises gamma phase constituents.

14. The method of claim 9, wherein conditioning the mixed-material vehicle scrap comprises heating the mixed-material vehicle scrap to a temperature between about 450 C. and about 600 C. for up to about 60 minutes.

15. The method of claim 9, wherein the mixed-material vehicle scrap is heated to above 700 C. and the aluminum alloy becomes molten.

16. A method of processing mixed-material vehicle scrap, the mixed-material vehicle scrap comprising aluminum parts and steel parts, the aluminum parts comprising an aluminum alloy and each of the steel parts comprising a steel substrate and a coating, the method comprising: conditioning the mixed-material vehicle scrap by heating the mixed-material vehicle scrap to a temperature between about 450 C. and about 600 C. for up to about 60 minutes such that iron from each of the steel parts is diffused into each of the coatings to form a gamma phase diffusion layer, the gamma phase diffusion layer comprising intermetallic constituents and having a melting temperature greater than a melting temperature of the aluminum alloy; heating the mixed-material vehicle scrap to a temperature above the melting temperature of the aluminum alloy and below the melting temperature of the diffusion layer, thereby allowing the steel parts to separate from the aluminum parts.

17. The method of claim 16, wherein the coating is applied with an electrocoating process.

18. The method of claim 16, wherein the coating comprises a zinc alloy.

19. The method of claim 16, wherein the coating has a thickness between about 2 microns and 10 microns.

20. The method of claim 16, wherein the diffusion layer has a thickness between about 2 microns and 10 microns.

Description

DRAWINGS

[0014] In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

[0015] FIG. 1 is a cross-sectional view of a self-piercing rivet, according to one aspect of the present disclosure;

[0016] FIG. 2 is a flowchart illustrating a method for recycling mixed alloy scrap in accordance with the principles of the present disclosure;

[0017] FIG. 3 is a microscopic image of an iron-zinc diffusion layer; and

[0018] FIG. 4 is an iron-zinc phase diagram according to the present disclosure.

[0019] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

[0020] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0021] Aluminum alloys are used in significant quantities in motor vehicles, both for body and frame parts. Because recycling aluminum takes 95% less energy than producing aluminum from raw materials, vehicle scrap is often recycled at the end of the life of a motor vehicle. During the recycling process, the scrap is separated by type of metal as far as possible, and the aluminum scrap is melted into a bath. In order to separate various materials in vehicle scrap, vehicles at the end of life are typically shredded and then separated by automated methods including weight separation and magnetic separation. However, parts that are small and/or tightly connected to aluminum parts, such as fasteners, often slip past the separation processes and remain with the aluminum. Although fasteners could be manually removed, such as by drilling out for example, it would not be efficient for the majority of circumstances.

[0022] The quality and utility of the recycled aluminum alloy is dependent on the composition, especially the iron content. Above 0.6 wt. % iron content, the ductility of the resulting aluminum alloy is reduced below the requirements for use in motor vehicles. The higher quality recycled aluminum alloys have less than 0.2 wt. % iron. Because higher amounts of iron produce alloys which lack the desired formability and structural properties for applications in motor vehicles, methods of limiting iron transfer from steel fasteners and other steel parts into the aluminum alloy parts are provided by the teachings herein.

[0023] Referring now to FIG. 1, an exemplary fastener is referred to by reference numeral 10 and shown in cross section. As illustrated, the fastener 10 is a self-piercing rivet; however, a variety of fastener types may be used within the scope of the present disclosure. The fastener 10 is used to join aluminum parts 12, by way of example. The aluminum parts 12 are aluminum motor vehicle parts such as aluminum panels, frames, and the like. The fastener 10 includes a steel substrate 14 and a coating 16 disposed around the substrate. Thus, the fastener 10 and the aluminum parts 12 are mixed-material because they are made from different materials, e.g., aluminum, steel, and the coating as set forth below.

[0024] In one variation, the coating is applied with an electrocoating process, which may be an electrogalvanized zinc or a zinc alloy. The thickness of the zinc coating is typically between 2 and 10 microns. In another form, the coating is a nickel coating with a thickness between 1 and 5 microns. In addition, other metal coatings may be used, with the electrocoating process or other coating process, while remaining within the scope of this disclosure. For example, these other metal coatings include but are not limited to cadmium, magnesium, or manganese, among others.

[0025] Referring to FIG. 2, the present disclosure provides a novel method 20 of recycling a collection of mixed-material vehicle scrap, such as by way of example the aluminum parts 12 with coated steel fasteners 10 set forth above. The mixed-material vehicle scrap is made up of a first group of parts and a second group of parts.

[0026] The first group of parts includes scrap from bulk parts such as vehicle panels, frames, and panels (e.g., the aluminum parts 12). Generally, the first group of parts is made of a first alloy. In one form, the first group of parts comprises an aluminum alloy as set forth above, but other materials may be employed for the first alloy, such as by way of example, magnesium, while remaining within the scope of the present disclosure.

[0027] The second group of parts are small components which cannot be easily separated from the first group of parts, including fasteners 10 as set forth above and shown in FIG. 1. Each of the second group of parts includes a substrate and a coating disposed over the substrate. Generally, the substrate is made of a second alloy. The second alloy includes components which should be limited in the recycled aluminum or other first alloy, such as but not limited to iron. In one form, the substrate is a steel alloy and the coating is a zinc alloy, as previously described. Other materials, such as, for example, non-steel iron alloys or non-ferrous alloys, may be employed while remaining within the scope of the present disclosure.

[0028] As shown in FIG. 2, the first step of the method is conditioning, or heating, the mixed-material vehicle scrap. In one form, the conditioning is done by heating the mixed material vehicle scrap to a temperature between about 450 C. and about 600 C. for up to about 60 minutes. During the conditioning, iron from the steel substrate is diffused into the coating on the second group of parts to form a diffused coating on each part. For example, iron from the steel substrate 14 of the fastener 10 is diffused into the coating 16 of the fastener 10. More generally, a component or chemical element of the second alloy is diffused from the substrate into the coating to form the diffused coating. The diffused coating has a melting temperature greater than a melting temperature of the substrate and greater than the melting temperature of the aluminum or other first alloy. As set forth in more detail below, the difference in melting temperature inhibits melting of the second alloy into the first alloy and allows separation of the first group of parts from the second group of parts.

[0029] In one specific form in which the second alloy is steel and the coating is zinc, iron from the steel diffuses into the zinc coating to form a diffused coating with a zinc-iron solid solution diffusion layer. The zinc-iron diffusion layer includes layers of intermetallic constituents made up of different alloy phases as the percentage of iron within the zinc changes. The zinc-iron diffusion layer does not react with the aluminum.

[0030] In one form, the diffused coating contains a gamma phase diffusion layer made up of gamma phase intermetallic constituents. FIG. 3 shows an example of a zinc-iron diffusion layer including a gamma phase diffusion layer indicated by reference numeral 20. The gamma phase intermetallic constituents of the zinc-iron layer have a higher melting temperature than the melting temperature of aluminum and/or the temperature of an aluminum recycling bath. FIG. 4 shows a zinc-iron phase diagram which illustrates that the melting point of the gamma phase is 782 C.

[0031] In other variations, in which the substrate or the coating has a different composition, the diffused coating includes a different solid solution diffusion layer including intermetallic constituents in phase layers. For example, if the second alloy forming the substrate is a magnesium alloy and the coating is a nickel alloy, magnesium diffuses into the nickel layer to form a nickel-magnesium diffusion layer. As with the zinc-iron diffusion layer, other variations on the diffused coating do not react with the first alloy and have a melting temperature higher than the melting temperature of the aluminum or other first alloy. In one form, the diffusion layer has a thickness of between 2 and 10 microns, dependent on the temperature and length of the conditioning.

[0032] Referring back to FIG. 2, in a next step of the method, the conditioned mixed-material vehicle scrap is heated to a temperature above the melting temperature of the first alloy and below the melting temperature of the diffused coating. As a result, the first group of parts becomes molten. For example, the aluminum and steel scrap is heated to a temperature which melts the aluminum first group of parts into an aluminum bath. In one form, aluminum bath and the mixed-material vehicle scrap is heated to above 700 C. Because the second group of parts has a diffused coating with a melting temperature higher than the bath temperature, the diffused coating provides a barrier between the molten aluminum and the steel substrate. The diffused coating limits the amount of iron which mixes with the molten aluminum from the second group of parts. In one form, the second group of parts are separated from the molten aluminum. The steel fasteners are denser than the aluminum and therefore sink to the bottom of the aluminum bath where they can be collected and removed. Other methods of separation may include a magnetic collector.

[0033] Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word about or approximately in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability.

[0034] As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean at least one of A, at least one of B, and at least one of C.

[0035] The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.