JP2008280565A - Magnesium alloy and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium alloy having high strength and excellent corrosion resistance and capable of substituting for aluminum alloys and also to provide its manufacturing method. <P>SOLUTION: The magnesium alloy has a composition consisting of, by weight, 5 to 20% gadolinium, 0.1 to 5% of at least one element among zinc, silver and copper and the balance magnesium and further containing, if necessary, <1.5 wt.% zirconium. In this manufacturing method, the above magnesium alloy is subjected to solution heat treatment at 400 to 550°C treatment temperature and then aging heat treatment at 180 to 250°C treatment temperature. If necessary, e.g. for the removal of internal defects, HIP treatment is applied, before the above solution heat treatment, at 400 to 550°C treatment temperature and 0.05 to 1 GPa treatment pressure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high-strength magnesium alloy having excellent corrosion resistance and a method for producing the same.

  Magnesium is lightweight, with a density that is one-fourth that of iron and two-thirds that of aluminum. Therefore, when applied to transportation equipment such as aircraft and automobiles, magnesium saves energy and reduces CO2 emissions. Can be expected.

  When assuming the replacement of the aluminum alloy with the magnesium alloy, if the specific strength of the magnesium alloy (ratio of strength and density) is 130% or more of the assumed aluminum alloy in the strength characteristics, it can be replaced without changing the shape of the member, In addition, since about 30% of the member can be reduced in weight, such a magnesium alloy is a practically very effective material.

  As a magnesium alloy that has already been put into practical use, there is an Mg—Al—Zn—Mn alloy (AZ91 alloy: Al 9%, Zn: 1%, Mn: 0.35%).

  Patent Documents 1 and 2 propose Mg-Gd-Y alloys as magnesium alloys with improved strength characteristics and heat resistance.

  Patent Document 3 proposes an Mg-Al-Zn-Y alloy as a magnesium alloy with improved corrosion resistance.

Japanese Patent Laid-Open No. 6-49579 Japanese Patent Laid-Open No. 10-147830 Japanese National Patent Publication No. 3-503661

  However, the above magnesium alloy has the following problems.

  Since Mg—Al—Zn—Mn alloys such as AZ91 alloy have low strength characteristics and insufficient corrosion resistance, it is impossible to substitute them without changing the shape even in low strength aluminum alloys.

  Moreover, although the intensity | strength of the Mg-Gd-Y type alloy of patent document 1 and patent document 2 is as high as about 360 MPa, there is no description about corrosion resistance, and it is unknown.

  Moreover, although the Mg-Al-Zn-Y-based alloy of Patent Document 3 has improved corrosion resistance as compared with the Mg-Al-Zn-Mn-based alloy, the strength is as low as about 280 MPa, and there is no change in shape as a structural member. It is impossible to replace aluminum alloys.

  Therefore, the inventors of the present application have made a magnesium-gadolinium alloy (Mg-Gd alloy) zinc (Zn), silver (Ag), and copper (Cu) as a magnesium alloy that has comprehensively improved strength characteristics and corrosion resistance. As a result, an alloy composition having strength properties and corrosion resistance that can replace aluminum alloys has been found.

  That is, an object of the present invention is to provide a high-strength magnesium alloy with excellent corrosion resistance that can solve the above problems and can replace an aluminum alloy, and a method for producing the same.

  In order to achieve the above object, the invention according to claim 1 contains 5 to 20% by weight of gadolinium, 0.1 to 5% by weight of at least one of zinc, silver and copper, with the balance being magnesium. This is a magnesium alloy characterized in that

  The invention according to claim 2 is the magnesium alloy according to claim 1 containing zinc and silver or zinc and copper in a total amount of 0.1 to 5% by weight.

  The invention according to claim 3 is the magnesium alloy according to claim 1 or 2 containing less than 1.5% by weight of zirconium.

  The invention according to claim 4 contains 0.5 to 4% by weight of zinc and 0.2 to 1% by weight of zirconium so that the specific strength is 130% or more of the A201 alloy. It is an alloy.

  The invention according to claim 5 contains 0.1 to 5% by weight of silver and 0.2 to 1% by weight of zirconium so that the specific strength is 130% or more of the AC4C alloy. It is an alloy.

  The invention according to claim 6 is the magnesium according to claim 3, which contains 0.1 to 5% by weight of copper and 0.2 to 1% by weight of zirconium so that the specific strength is 130% or more of the AC4C alloy. It is an alloy.

  A seventh aspect of the present invention is a method for producing a magnesium alloy, comprising subjecting the magnesium alloy according to any one of the first to sixth aspects to a solution treatment, followed by an aging heat treatment.

  The invention according to claim 8 is the method for producing a magnesium alloy according to claim 7, wherein the treatment temperature of the solution treatment is 400 to 550 ° C, and the treatment temperature of the aging heat treatment is 180 to 250 ° C.

  In the invention according to claim 9, before the solution treatment, HIP treatment (hot isostatic pressing, hot isostatic pressing method) with a treatment temperature of 400 to 550 ° C. and a treatment pressure of 0.05 to 1 GPa is performed. A method for producing a magnesium alloy according to claim 7 or 8.

  The invention according to claim 10 is the method for producing a magnesium alloy according to any one of claims 7 to 9, wherein a rolling treatment is performed before the solution treatment.

  According to the present invention, the excellent effect of being excellent in corrosion resistance and having high strength and being able to replace an aluminum alloy is exhibited.

  Hereinafter, a preferred embodiment of the present invention will be described in detail.

  The magnesium alloy of the present invention contains 5 to 20% by weight of gadolinium, 0.1 to 5% by weight of at least one of zinc, silver and copper, and the balance is composed of magnesium and inevitable impurities. is there.

  When gadolinium is added to magnesium, it has the effect of improving strength characteristics and corrosion resistance. However, when added too much, the density increases and the lightness is lost, and an intermetallic compound appears and the strength decreases.

  Therefore, the content of gadolinium was set to 5 to 20% by weight as a range in which excellent corrosion resistance and high strength were exhibited while maintaining lightness.

  This is because if the gadolinium content is less than 5% by weight, the strength characteristics and corrosion resistance are not sufficiently improved. On the other hand, if it exceeds 20% by weight, the magnesium alloy becomes heavy, and the strength decreases due to the intermetallic compound. It is because it ends up.

  In addition, when zinc, silver, and copper are added to magnesium in combination with gadolinium, a special structure with periodicity appears at the atomic level, and the effect of further improving the strength characteristics can be expected. An intermetallic compound precipitates at the grain boundary, causing a decrease in strength characteristics.

  Therefore, the magnesium alloy of the present invention contains at least one of zinc, silver, and copper in an amount of 0.1 to 5% by weight.

  This is because when the content of at least one of zinc, silver and copper is less than 0.1% by weight, the strength characteristics are not sufficiently improved, whereas when the content exceeds 5% by weight, the strength is increased by the intermetallic compound. It is because it will fall.

  The magnesium alloy of the present invention contains less than 1.5% by weight of zirconium as a structure refining material for refining crystal grains and improving strength characteristics.

  The reason why the zirconium content is less than 1.5% by weight is that when the zirconium content is 1.5% by weight or more, a compound composed of zirconium and an alloy element is generated and the characteristics of the alloy are deteriorated. is there.

  By adjusting the types and amounts of the additive elements (Gd, Zn, Ag, Cu, Zr) described above, it is possible to provide an alloy that matches the balance of strength and ductility of the aluminum alloy that is desired to be replaced.

  For example, a magnesium alloy that replaces the A201 alloy (ASTM standard), which is a high-strength aluminum alloy, contains 0.5 to 4% by weight of zinc and 0% of zirconium so that the specific strength is 130% or more of the A201 alloy. Those containing 2 to 1% by weight are preferred.

  As a magnesium alloy that replaces the AC4C alloy (JIS standard), which is a general-purpose aluminum alloy, 0.1 to 5% by weight of silver and 0.2 to 0.2% of zirconium are included so that the specific strength is 130% or more of the AC4C alloy. Those containing 1% by weight, or those containing 0.1 to 5% by weight of copper and 0.2 to 1% by weight of zirconium are preferred.

  Next, the manufacturing method of the magnesium alloy which concerns on this invention is demonstrated.

  First, a magnesium alloy material consisting of 5 to 20% by weight of gadolinium, 0.1 to 5% by weight of at least one of zinc, silver and copper and the balance of magnesium is melted, and the molten metal is used as a mold (sand mold, gypsum). Mold, mold, etc.) and cast magnesium alloy.

  Next, a solution treatment of the cast magnesium alloy (cast product) is performed, and then an aging heat treatment of the solution-treated magnesium alloy is performed.

  Specifically, after the solution treatment is performed at a processing temperature of 400 to 550 ° C. for 2 to 24 hours, the aging heat treatment is performed at a processing temperature of 180 to 250 ° C. for 8 to 100 hours. The treatment time for solution treatment and aging heat treatment is appropriately set in consideration of the size and shape of the alloy.

  Thus, by performing heat treatment (solution treatment and aging heat treatment) after casting, the alloy becomes a structure in which fine aging precipitates are generated inside the crystal, and the tensile strength is improved to about 400 MPa at the maximum. Can do.

  Furthermore, you may make it express higher intensity | strength by performing a rolling process before solution treatment. Here, the rolling treatment is preferably a hot rolling treatment at a treatment temperature of 300 to 520 ° C.

  When the rolling treatment is performed in this way, the intermetallic compound generated at the grain boundary can be finely and uniformly dispersed, so that the tensile strength is higher than that of the cast product, and the tensile strength property of about 450 MPa. Can be expressed.

  Further, if necessary, for example, for removing internal defects, the cast magnesium alloy may be subjected to HIP treatment before the solution treatment. The HIP treatment is performed at a treatment temperature of 400 to 550 ° C. and a treatment pressure. Is preferably carried out at 0.05 to 1 GPa.

  According to the present invention described above, strength characteristics are improved, and a casting made of a magnesium alloy reaches a level at which a general-purpose aluminum alloy casting can be replaced without changing its shape. At the same time, the magnesium alloy of the present invention can improve the corrosion resistance, and can realize a magnesium alloy having both strength and corrosion resistance.

  Moreover, since it does not contain yttrium, flux refining becomes possible, and the cleanliness (purity) of the magnesium alloy can be increased.

  In addition, this invention is not limited to the above-mentioned embodiment, Various modifications and application examples can be considered.

  For example, a magnesium alloy containing two or three of zinc, silver, and copper is conceivable. Specifically, one containing zinc and silver or zinc and copper in a total amount of 0.1 to 5% by weight. Conceivable.

  Also, gadolinium can be used in other R. E. It is also conceivable to substitute with a composite addition of an element and gadolinium. E. The total amount of elements is preferably 5 to 20% by weight.

  Next, examples of the magnesium alloy according to the present invention will be described.

  Table 1 shows the results of tests on tensile strength (tensile strength), 0.2% proof stress, and elongation at break for an alloy for replacing a high-strength aluminum alloy (for example, A201 alloy).

  In Examples 1 to 4 and Comparative Example 1 in Table 1, a magnesium alloy was cast with the composition shown in Table 1, and the cast product was subjected to a solution treatment of 515 ° C. × 8 h + 520 ° C. × 8 h, then 225 ° C. × 8 h. The aging heat treatment was performed. As the casting mold, a sand mold was used in Example 2, and a mold was used in Examples 1, 3, 4 and Comparative Example 1 other than that.

  As shown in Table 1, the alloys of Examples 1 to 4 have a good tensile strength of 363 to 400 MPa, and have achieved a tensile strength of about 400 MPa. The 0.2% proof stress was also good at 272 to 278 MPa, and the elongation at break was also good at 1 to 2.9%.

  From the above, it was confirmed that Examples 1 to 4 have sufficient strength characteristics to replace the high-strength aluminum alloy.

  On the other hand, the alloy of Comparative Example 1 had a tensile strength as low as 105 MPa because the zinc content exceeded 5.0%. The 0.2% proof stress was 248 MPa, which was lower than those of Examples 1 to 4, and the elongation at break was 5.2%, which was larger than those of Examples 1 to 4.

  Table 2 shows the results of tests for tensile strength, 0.2% proof stress, and elongation at break for an alloy for substituting a general-purpose aluminum alloy (for example, AC4C alloy).

  In Examples 5 and 6 and Comparative Examples 2 and 3 in Table 2, a magnesium alloy having a composition shown in Table 2 was cast with a mold, and the cast product was subjected to a solution treatment of 430 ° C. × 24 h. Aging heat treatment was performed for 8 hours.

  As shown in Table 2, the alloys of Examples 5 and 6 had good tensile strength of 378 to 393 MPa. The 0.2% proof stress was also good at 276 to 278 MPa, and the elongation at break was also good at 1.3 to 1.8%.

  From the above, it was confirmed that the alloys of Examples 5 and 6 had sufficient strength characteristics to replace the general-purpose aluminum alloy.

  On the other hand, although the alloy of Comparative Example 2 has a good 0.2% proof stress of 291 MPa and a breaking elongation of 1.3%, since the silver content exceeds 5.0%, the tensile strength is 253 MPa. It was low.

  Further, although the alloy of Comparative Example 3 had a good 0.2% proof stress of 267 MPa and a breaking elongation of 1.0%, the tensile strength was as low as 220 MPa because the copper content exceeded 5.0%. .

  Thus, it was confirmed that when the amount of zinc, silver, and copper is large (over 5.0%), the strength of the alloy decreases.

  Next, as shown in FIG. 1, a salt spray test according to JIS Z 2371 was performed to confirm corrosion resistance.

  In the graph of FIG. 1, the horizontal axis represents time (h), and the vertical axis represents corrosion weight loss (mg / cm 3). In this graph, the cross marks indicate A201-T7 alloy (ASTM standard), which is a high-strength aluminum alloy, the circle marks indicate AZ91-T6 alloy (ASTM standard), and the square marks indicate Example 1.

  The salt spray test was performed by spraying a 50 ± 5 g / L NaCl solution at 35 ° C. ± 1 ° C. and measuring the average corrosion weight loss at predetermined intervals.

  As shown in FIG. 1, the corrosion resistance of Example 1 is significantly improved compared to the AZ91-T6 alloy (conventional magnesium alloy) and has a corrosion resistance characteristic approaching that of the A201-T7 alloy (high-strength aluminum alloy). .

  From the above, it was confirmed that the magnesium alloy of the present invention has good corrosion resistance comparable to that of the aluminum alloy.

  Next, as shown in FIG. 2, a high temperature tensile test was performed to confirm heat resistance.

  FIG. 2 shows the results of measurement of yield stress (YS), maximum tensile stress (UT), and fracture elongation at 25 to 250 ° C., and the horizontal axis represents temperature (° C.). The left vertical axis is the yield stress (Pa) and the maximum tensile stress (Pa), and the right vertical axis is the breaking elongation (%).

  In FIG. 2, circles indicate yield stress, triangles indicate maximum tensile stress, squares indicate elongation at break, white indicates Example 1, and black indicates a HIP-treated product obtained by subjecting Example 1 to HIP treatment. Show.

  The HIP treatment was performed at 505 ° C. × 0.1 GPa before the solution treatment.

  As shown in FIG. 2, in both Example 1 and the HIP-treated product, no decrease in strength was observed for yield stress and elongation at break up to 150 ° C., and a decrease in strength was observed until about 200 ° C. for maximum tensile stress. There wasn't.

  From the above, it was confirmed that the magnesium alloy of the present invention showed good heat resistance.

  Further, at 25 ° C., it was confirmed that the HIP-treated product had higher strength characteristics than those of Example 1.

FIG. 1 is a graph for explaining the average corrosion weight loss by a salt spray test of a magnesium alloy according to the present invention. FIG. 2 is a graph for explaining the high-temperature tensile properties of the magnesium alloy according to the present invention.

Claims (10)

  A magnesium alloy containing 5 to 20% by weight of gadolinium, 0.1 to 5% by weight of at least one of zinc, silver and copper, and the balance being magnesium.   The magnesium alloy according to claim 1, containing zinc and silver or zinc and copper in a total amount of 0.1 to 5% by weight.   The magnesium alloy according to claim 1 or 2, which contains less than 1.5% by weight of zirconium.   The magnesium alloy according to claim 3, containing 0.5 to 4% by weight of zinc and 0.2 to 1% by weight of zirconium so that the specific strength is 130% or more of the A201 alloy.   The magnesium alloy according to claim 3, which contains 0.1 to 5% by weight of silver and 0.2 to 1% by weight of zirconium so that the specific strength is 130% or more of the AC4C alloy.   The magnesium alloy according to claim 3, containing 0.1 to 5% by weight of copper and 0.2 to 1% by weight of zirconium so that the specific strength is 130% or more of the AC4C alloy.   A method for producing a magnesium alloy, comprising subjecting the magnesium alloy according to any one of claims 1 to 6 to a solution treatment, and thereafter performing an aging heat treatment.   The method for producing a magnesium alloy according to claim 7, wherein a treatment temperature of the solution treatment is 400 to 550 ° C, and a treatment temperature of the aging heat treatment is 180 to 250 ° C.   The manufacturing method of the magnesium alloy of Claim 7 or 8 which performs the HIP process of process temperature 400-550 degreeC and process pressure 0.05-1GPa before the said solution treatment.   The manufacturing method of the magnesium alloy in any one of Claim 7 to 9 which performs a rolling process before the said solution treatment.

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