JP2008254003A - Method for manufacturing clad material, and clad material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a clad material, which manufactures a clad plate by covering the surface of a magnesium-lithium-based alloy plate with an aluminum or aluminum alloy plate and imparts excellent strength, lightness, cold workability, and corrosion resistance to the clad material, and which manufactures it at more advantageous cost than conventional joining techniques of rolling, and to provide a clad material. <P>SOLUTION: An objective clad material is obtained by superimposing an aluminum or aluminum-alloy plate on a magnesium-lithium-based alloy plate, subjecting them to overlap joining by friction stirring, and rolling them. It is preferable that the overlap joining by friction stirring is closely applied to the whole surface of the plates. The rolling operation is preferably conducted a plurality of times in a cold condition (at room temperature). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a clad material in which a surface of a magnesium-lithium alloy plate is covered with a plate of aluminum or an alloy thereof, and a clad material.

  Commonly used magnesium-based alloys (mainly containing Al and Zn as additive elements) are lighter than aluminum and its alloys and have higher specific strength and specific rigidity than aluminum and its alloys. It is used as a structural material for parts, bicycle parts, and various electrical product bodies.

  This type of magnesium-based alloy has a close-packed hexagonal crystal structure and therefore has poor ductility and poor plastic workability at room temperature. Magnesium-lithium alloys, on the other hand, have a eutectic structure with a close-packed hexagonal structure and a body-centered cubic structure due to the inclusion of lithium, so the slip on the crystal plane is improved, and press working and drawing at room temperature. Such plastic processing is possible, and future development as a structural material is expected.

  However, in order to use as a structural material, it is necessary to have corrosion resistance in addition to strength, lightness, and plastic workability at room temperature. However, since magnesium-lithium alloys contain lithium, they have poor corrosion resistance. For example, when they are placed in the atmosphere or in an environment where they come into contact with salt water, there is a large practical problem that the surface becomes gray and corrodes.

  In the following Patent Document 1, an aluminum or aluminum alloy plate is superposed on the surface of a magnesium-lithium alloy base material, and this is rolled and joined at room temperature to 300 ° C. An aluminum-coated magnesium-lithium alloy base material (cladding material) excellent in corrosion resistance in addition to strength, lightness, and plastic workability at room temperature by heat treatment, and a method for producing the same have been proposed.

  However, in the above proposal, as described in the examples, the surface where the magnesium-lithium alloy base material and the plate of aluminum or its alloy are in contact is pickled in advance, and further a metal wire brush. Good adhesion cannot be obtained unless it is cleaned by removing the oxide film and the like. Therefore, there is a problem that environmental equipment is required, the cleaning process before the rolling operation is troublesome, and the manufacturing cost of the clad material increases.

  Furthermore, in the above proposal, a practically strong joining force cannot be obtained at a rolling temperature of room temperature. As described in the examples, when rolling at room temperature, about 150 to 300 ° C. after rolling. Therefore, it is necessary to increase the bonding strength and bend formability by performing a heat treatment for a long time (about 1 hour) at this temperature. In this respect as well, there is a problem that the manufacturing cost increases due to the reason of the process and equipment.

  In addition, if heating is performed at a relatively high temperature of about 200 to 300 ° C. for a long time during rolling or heat treatment, a brittle intermetallic compound is easily generated at the bonding interface, and the bonding strength is not much improved. In addition, cracks may occur in the bending test of the obtained clad material.

In Patent Document 2 below, a normal magnesium alloy plate (mainly containing Al or Zn as an additive element) and an aluminum alloy plate are overlapped, and this is overlapped and joined by friction stirring. According to the above, it is described that a structure of a railway vehicle or the like is manufactured. It does not suggest the invention to be produced. Nor does it suggest the use of a magnesium-lithium alloy plate.
JP 2004-323935 A JP 2005-40851 A

  The present invention has been made in view of the above problems, and an object of the present invention is a clad material in which a surface of a magnesium-lithium alloy plate is coated with aluminum or a plate of the alloy, and has a strength and a lightness. Another object of the present invention is to provide a clad material manufacturing method and a clad material which are excellent in corrosion resistance in addition to plastic workability at room temperature and also advantageous in cost.

The above object can be achieved by a method for producing a clad material having the following characteristics and the clad material.
In other words, the method for producing a clad material according to claim 1 of the present invention includes superimposing a magnesium-lithium alloy plate and an aluminum plate or an alloy plate thereof, superposing and joining them by friction stirring, and then rolling. Features.

  The method for manufacturing a clad material according to claim 2 of the present invention is characterized in that, in the method for manufacturing a clad material according to claim 1, lap joining by friction stirring is performed over the entire surface of the plate without a gap.

  The method for manufacturing a clad material according to claim 3 of the present invention is characterized in that, in the method for manufacturing a clad material according to claim 1 or 2, the same portion is subjected to frictional stirring a plurality of times.

  A method for producing a clad material according to a fourth aspect of the present invention is characterized in that in the method for producing a clad material according to any one of the first to third aspects, cold rolling is performed a plurality of times.

  A clad material according to claim 5 of the present invention is obtained by the method for producing a clad material according to any one of claims 1 to 4.

  In the present invention, the magnesium-lithium alloy includes an alloy containing magnesium as a main component and containing lithium in order to impart plastic workability at room temperature thereto. In addition, it contains magnesium as a main component and imparts plastic workability at room temperature to it, and in order to improve heat resistance and toughness, a smaller amount of aluminum, zinc, manganese, yttrium, Examples include alloys containing metals such as lanthanoids, zirconium, silver, silicon, and calcium.

  Here, lithium is preferably contained within a range of 5 to 15% by weight. If the lithium content is less than 5% by weight, the plastic workability at room temperature is not improved so much. Conversely, if the lithium content exceeds 15% by weight, the crystal grains become coarse during friction stir welding or rolling. It may cause a grain boundary crack (surface crack), and the cost is high because lithium is expensive. In particular, LA141 (Mg-14% Li-1% Al alloy) and LW91 (Mg-9% Li-1% Y alloy) standardized by ASTM, Mg-Li alloy, Mg-Li-Zn alloy Are preferably used.

  In the present invention, as aluminum or an alloy thereof, pure aluminum (1000 series), Al-Cu alloy (2000 series), Al-Mn alloy (3000 series), Al-Si alloy (4000 series), Al-Mg based alloys (5000 series), Al-Mg-Si based alloys (6000 series), Al-Zn-Mg based alloys, Al-Zn-Mg-Cu based alloys (7000 series), etc. are particularly limited. Not.

  In the present invention, a magnesium-lithium alloy plate and aluminum or an alloy plate thereof are superposed, superposed and joined by friction stirring, and then rolled. The thickness of the magnesium-lithium-based alloy plate is not particularly limited, but a thickness of about 3 to 10 mm is generally used in consideration of the rolling rate for use as a structural material. Also, the thickness of the aluminum or its alloy plate is not particularly limited, but it is intended to provide corrosion resistance by covering the surface of the magnesium-lithium alloy plate, so it is thinner than the thickness of the magnesium-lithium alloy plate, Considering the rolling rate, generally a thickness of about 0.5 to 6 mm is used.

  In the present invention, the friction stir welding is performed using a known friction stir welding apparatus equipped with a tool having a large-diameter shoulder surface and a small-diameter probe projecting from the center of the surface. The tool is made of tool steel or WC superhard material that is harder than the plate materials to be joined. It is preferable that the probe is not formed with a thread (thread) so that the overlapped plate material is not excessively stirred and diffused up and down, but a thread may be formed. In addition, the shoulder surface may be a flat surface, but normally, a concave surface that is slightly arcuate or conical about the probe is used so that the thickness of the joint portion is not reduced. Here, the diameter of the shoulder surface of the tool is preferably about 12 to 25 mm, and the diameter of the probe is preferably about 4 to 10 mm.

  The friction stir welding operation is performed by first placing and fixing the magnesium-lithium alloy plate and the aluminum or alloy plate on the surface plate of the friction stir welding apparatus. Then, press the probe of the tool that rotates at high speed from the surface of the upper plate (aluminum or its alloy plate) with a predetermined load and insert it from the upper plate to the vicinity of the lower plate (magnesium-lithium alloy plate). , Move the tool or plate relatively. Then, both the plate material in the vicinity of the probe softens and plastically flows due to the rotational frictional heat of the probe, and the softened plate material is prevented from being discharged outward by the shoulder surface of the tool. The upper and lower plates are joined together by frictional heat.

  Here, there is no defect such as a crack on the surface of the joint portion, and the plate material is not excessively stirred and diffused up and down on the joint surface, and the tool rotation speed is 600 to 1800 pm, the joint speed ( The feed rate of the tool is 50 to 500 mm / min, and the length of the probe of the tool is 0 to about 0.6 mm smaller than the thickness of the upper plate (aluminum or its alloy plate) into which the probe is inserted. It is preferable to set the length within a range of about 2 mm. Normally, the load of the tool is preferably set to 0.5 to 3 tons, and the advance angle of the tool is preferably set to about 3 to 5 °. Under such conditions, good solid phase bonding is performed in a state where the maximum temperature (peak temperature) of the plate material by friction stirring is suppressed to 250 ° C. or less, and almost no brittle intermetallic compound is generated at the joint. .

  The superposition joining by the friction stirrer can be performed even if it is performed in an arbitrary pattern with a gap such as a parallel shape, a lattice shape, a spiral shape, or a spot shape on the plate. However, it is preferable that the overlap bonding is performed without any gap over the entire surface of the portion to be rolled. This is because if there is a portion that is not overlap-bonded, the portion is peeled off by rolling.

  Further, when the same portion is subjected to frictional stirring a plurality of times, that is, when the stirring region generated by frictional stirring is further subjected to frictional stirring, it is preferable because the crystal of the joint is refined and the strength and hardness of the joint are improved. In addition, if the friction stir is performed while slightly shifting in the width direction of the joint portion so that the joint portion partially overlaps in the width direction in order to increase the width of the joint portion, the joint portion expands in the width direction without gaps and the strength of the joint portion And the hardness is also improved.

  Rolling is performed after the friction stir welding. This rolling operation is performed at a temperature of room temperature to 200 ° C., preferably cold (room temperature), using a known rolling device composed of a rolling roll or the like. When the rolling temperature exceeds 200 ° C., brittle intermetallic compounds are likely to be formed at the bonding interface, and the bonding force tends to be reduced. In the obtained bending test of the clad material, intergranular cracking occurs outside the part to be bent. May occur. In the present invention, since strong joining is performed by friction stir welding before rolling, a strong joining force can be maintained even if the subsequent rolling is performed cold (room temperature). In addition, it is preferable to sequentially reduce the thickness by a plurality of rollings and adjust the thickness to a desired plate thickness in order to reliably prevent cracks during the rolling operation, but it may be a single rolling.

  In the present invention, the rolling rate is preferably 20 to 80% per rolling. When the rolling rate is less than 20% per rolling, the effect of reducing the crystal grain size or the variation of crystal grains becomes small, and the strength and hardness are not improved so much. On the other hand, if the rolling rate exceeds 80% per rolling, the plate material tends to break during the rolling operation. Here, a rolling rate means the decreasing rate of the thickness of the clad material before and behind rolling. That is, it is expressed as a percentage with respect to (thickness before rolling−thickness after rolling) / thickness before rolling.

  By such a rolling operation, the difference in the crystal grain size between the bonded portion by friction stirrer and the other unbonded portion is reduced, and also the bonding traces generated on the surface disappear, and both plate materials are laminated and bonded in layers. Thus, a clad material suitable for plastic working such as pressing or drawing at room temperature can be obtained. In addition, since strong joining is performed by friction stir welding, it is not necessary to heat-treat the clad material after rolling to increase the joining force and bending workability.

  According to the present invention, the upper and lower plate materials are appropriately stirred and diffused by friction stir and joined in a solid state, so that a magnesium-lithium alloy plate and aluminum or its alloy plate are used as in conventional rolling joining. The surface where the contact is made is pickled in advance and polished with a metal wire brush to remove the oxide film, etc., so that strong bonding can be achieved. Compared with conventional rolling bonding in this respect, the product Costs and manufacturing costs can be kept low.

  In addition, according to the present invention, since strong joining is performed by friction stir welding, the rolling performed after friction stir welding does not decrease because the joining force is maintained even when performed cold (room temperature). Unlike conventional rolling joining, there is no need to heat the clad material at a temperature of about 200 to 300 ° C. for a long time after rolling at room temperature to improve the joining force and bending workability. Product costs and manufacturing costs can be kept low compared to bonding.

  The clad plate obtained in this way is coated with aluminum or its alloy plate on the surface of the magnesium-lithium alloy plate, so that the strength, lightness and plasticity at room temperature are the same as the clad plate obtained by conventional rolling joining. In addition to workability, it has excellent corrosion resistance, and it is not necessary to increase the joining force and bending workability by heat treatment at a temperature of about 200 to 300 ° C. for a long time as in conventional rolling joining. Since there is no need for heat treatment as compared with rolling joining, brittle intermetallic compounds are less likely to be formed at the joining interface, and intergranular cracking is less likely to occur outside the part to be bent in the bending test of the clad material.

  In the conventional friction stir welding technique, there is a limitation in thinly coating a plate of aluminum or an alloy thereof. However, in the present invention, the entire surface is rolled and thinned after the friction stir welding. There is an advantage that the alloy plate can be thinly coated.

  Examples of the present invention will be given below. The present invention is not limited to these examples.

  A 1 mm thick aluminum plate (A5083) is superposed on the surface of a 3 mm thick magnesium-lithium alloy plate (LA141), and a tool (shoulder diameter 12 mm) having a threaded probe of length 1.2 mm × diameter 4 mm is provided. Using a tool rotation speed of 600 rpm, a welding speed of 100 mm / min, and a tool load of 2 ton, the tool is moved linearly relative to the material to be joined, and superposition joining is performed over 60 mm by one friction stir. It was. As a result, there were no defects such as cracks on the surface of the joint, and the LA141 plate (lower layer) and the A5083 plate (upper layer) were joined well without being mixed up and down at the joint surface.

  Under the same conditions as described above, the tool is shifted in parallel by 2 mm in the width direction with respect to the joint trace, and further moved by being shifted in parallel by 2 mm in the width direction with respect to the joint trace. Lamination bonding was performed. A surface photograph (magnification 1.2 times) after the three times of friction stir welding is shown in FIG. 1, a cross-sectional photograph (magnification 7 times) is shown in FIG. 2, and a cross-sectional photograph (magnification 50 times) is shown in FIG. . As is apparent from FIGS. 1 to 3, the surface of the joint is free from defects such as cracks, and the LA141 plate (lower layer) and the A5083 plate (upper layer) do not mix too much at the joint surface. It was joined.

  After the above three friction stir weldings, this was rolled once at room temperature (25 ° C.) at a rolling rate of about 30%. FIG. 4 shows a cross-sectional photograph (magnification 3.5 times) of the obtained rolled material, and FIG. 5 shows a cross-sectional photograph (magnification 50 times). As is apparent from FIG. 4 and FIG. 5, the bonding marks generated on the surface disappear, there are no defects such as cracks on the surface of the bonding portion, and the LA141 plate (lower layer) and the A5083 plate (upper layer) are layered. It was joined well in a laminated state. That is, a clad material in which the surface of the LA141 plate was coated with the A5083 plate was obtained.

  A 1 mm thick aluminum (A5083) plate is superimposed on the surface of a 3 mm thick magnesium-lithium alloy plate (LA141), and a screwless tool (shoulder diameter 12 mm) having a probe of length 0.6 mm × diameter 3.5 mm. ), And overlap welding by one friction stirring was performed over 50 mm under the conditions of a tool rotation speed of 1400 rpm, a welding speed of 300 mm / min, and a tool load of 2 ton. As a result, there were no defects such as cracks on the surface of the joint, and the LA141 plate (lower layer) and the A5083 plate (upper layer) were joined well without being mixed up and down at the joint surface.

  Under the same conditions as described above, the tool was shifted in parallel by 2 mm in the width direction with respect to the welding marks, and overlap welding was performed by friction stirring three times in total. FIG. 6 shows a surface photograph (magnification 1.5 times) after the three times of friction stir welding, and FIG. 7 shows a cross-sectional photograph (magnification 5 times). As is clear from FIGS. 6 and 7, the surface of the joint is free from defects such as cracks, and the LA141 plate (lower layer) and the A5083 plate (upper layer) do not mix too much at the joint surface. It was joined to.

  After the above three times of friction stir welding, this is rolled at a room temperature (25 ° C.) at a rolling rate of about 20% per rolling for a total of 5 times, and the surface of LA141 plate is coated with A5083 plate. A clad material (total thickness 1.0 mm) was prepared. A cross-sectional photograph (magnification 15 times) of the obtained clad material is shown in FIG. As can be seen from FIG. 8, the bonding marks generated on the surface disappear, the surface of the bonded portion has no defects such as cracks, and the LA141 plate (lower layer) and the A5083 plate (upper layer) are laminated and bonded in layers. It was well joined in the state. That is, a clad material in which the surface of the LA141 plate was coated with the A5083 plate was obtained.

The same operation as in Example 2 was performed except that the joining speed was changed to 500 mm / min and the joining length was changed to 40 mm.
A surface photograph (1.5 times magnification) after three times of friction stir welding is shown in FIG. 9, and a cross-sectional photograph (5 times magnification) is shown in FIG. As is clear from FIGS. 9 and 10, the surface of the joint is free from defects such as cracks, and the LA141 plate (lower layer) and the A5083 plate (upper layer) do not mix too much at the joint surface. It was joined to.

  After the above-mentioned three times of friction stir welding, this is rolled at a room temperature (25 ° C.) at a rolling rate of about 20% per rolling for a total of five times, and the surface of LA141 plate is coated with A5083 plate. A clad material (total thickness 1.0 mm) was prepared. FIG. 11 shows a cross-sectional photograph (50 times magnification) of the obtained clad material. As can be seen from FIG. 11, the bonding marks generated on the surface disappear, the surface of the bonded portion has no defects such as cracks, and the LA141 plate (lower layer) and the A5083 plate (upper layer)) are laminated in layers. In this state, it was well bonded. That is, a clad material in which the surface of the LA141 plate was coated with the A5083 plate was obtained.

In Example 1, it is the photograph (1.5 times magnification) which shows the surface of the junction part after performing friction stir welding 3 times. In Example 1, it is the photograph (7-times multiplication factor) which shows the cross section of the junction part after performing friction stir welding 3 times. In Example 1, it is the photograph (50-times multiplication factor) which shows the cross section of the junction part after performing friction stir welding 3 times. In Example 1, it is the photograph (magnification 3.5 times) which shows the cross section of the junction part of the clad material obtained by rolling after performing friction stir welding 3 times. In Example 1, it is the photograph (50-times multiplication factor) which shows the cross section of the junction part of the clad material obtained by rolling after performing friction stir welding 3 times. In Example 2, it is the photograph (1.5 times magnification) which shows the surface of the junction part after performing friction stir welding 3 times. In Example 2, it is the photograph (5 times magnification) which shows the cross section of the junction part after performing friction stir welding 3 times. In Example 2, it is a photograph (magnification 15 times) which shows the section of the joined part of the clad material obtained by rolling after performing friction stir welding three times. In Example 3, it is the photograph (1.5 times magnification) which shows the surface of the junction part after performing friction stir welding 3 times. In Example 3, it is a photograph (5 times magnification) which shows the cross section of the junction part after performing friction stir welding 3 times. In Example 3, it is a photograph (50-times multiplication factor) which shows the cross section of the junction part of the clad material obtained by rolling after performing friction stir welding 3 times.

Claims (5)

  A method for producing a clad material, comprising: superimposing a magnesium-lithium alloy plate and aluminum or a plate of an alloy thereof;   The method for producing a clad material according to claim 1, wherein the overlapping joining by friction stirring is performed over the entire surface of the plate without any gap.   The method for producing a clad material according to claim 1 or 2, wherein the same portion is subjected to friction stirring a plurality of times.   The method for producing a clad material according to any one of claims 1 to 3, wherein the cold rolling is performed a plurality of times. The clad material obtained by the manufacturing method of any one of Claims 1-4.