JP2007186794A - Zn ALLOY FOR DIE-CASTING AND Zn ALLOY DIE-CAST PRODUCT - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Zn alloy for die-casting which enables cavity defects occurring therein to be suppressed and the thickness thereof to be reduced as a result, and to provide a die-cast product. <P>SOLUTION: The Zn alloy for die-casting comprises, by weight, 3 to 5% Al, 0.03 to 0.06% Mg, 0.5 to 5% Cu, further 0.01 to 1.0% of misch metal composed of one or more rare earth elements, and the balance Zn with inevitable impurities. In the die-cast product obtained by using this alloy, cavity defects can be remarkably decreased. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a Zn alloy for die casting, and further relates to a Zn alloy die-cast product manufactured using the alloy.

  Zn alloys have excellent mechanical properties and castability, and are thin and have complex shapes and precise dimensions. Therefore, Zn alloys are widely used as alloys for die casting after Al alloys. In addition, Zn alloy for die casting is economical because it has a wide range of surface treatments, has excellent corrosion resistance, and has a low melting point, so it can be die-cast in a hot chamber. It has such advantages as. For this reason, Zn alloys for die casting are widely used in automobile-related parts, machine parts, building hardware, ornaments and the like.

  As die-cast Zn alloys for die casting, there are two types of Zn alloy blocks for die casting in which Al and Mg are added to Zn, and one type of Zn alloy block for die castings in which about 1 wt% of Cu is further added thereto. Further, although not JIS-formed, there are also known three types of mold alloys in which about 3 wt% of Cu is added to two types of Zn alloy ingots for die casting. Furthermore, Japanese Patent No. 2691488 discloses a die casting Zn alloy having improved fluidity by increasing the amount of Al added. Japanese Examined Patent Publication No. 8-14011 discloses a Zn alloy for die casting in which strength is improved by adding Cu or other elements.

Japanese Patent No. 2691488 Japanese Patent Publication No. 8-14011

  On the other hand, the Zn alloy has a drawback that the specific gravity is larger than other die-cast alloys such as Al alloy and Mg alloy, and resin materials. For this reason, the share of the Zn alloy for die castings is being squeezed under the influence of weight reduction of automobiles and machines. In order to make up for such drawbacks, it is necessary to manufacture a light-weight Zn alloy die-cast product and reduce its weight as much as possible.

  However, die-cast products tend to have a cavity defect called “nest” inside. As a result, mechanical strength and elongation are reduced. In addition, the yield decreases due to the occurrence of cavity defects on the surface of the product, and the blister defect due to the cavity defects generated in the thin product portion is caused. In the case of a Zn alloy die-cast product, when the thickness is generally 1 mm or less, surface abnormality due to a cavity defect becomes conspicuous, and hot water wrinkles due to insufficient fluidity occur, resulting in reduced productivity.

  An object of the present invention is to provide a die-casting Zn alloy that can suppress the generation of cavity defects and can be thinned, and further provides a Zn alloy die-cast product manufactured using the alloy.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have found that conventionally known die alloy for die casting, such as one kind of die casting Zn alloy ingot, two kinds of die casting Zn alloy ingots, and three kinds of mold alloys. It has been found that by adding an appropriate amount of rare earth element to a Zn alloy, the cavity defects in the Zn alloy die-cast product can be significantly reduced.

  Based on this knowledge, according to the present invention, Al: 3-5 wt%, Mg: 0.03-0.06 wt%, Cu: 0.5-5 wt%, one or more rare earth elements: 0.0. A Zn alloy for die casting is provided, which contains 01 to 1.0 wt%, and the balance is made of Zn and inevitable impurities.

  The rare earth element content is preferably less than 0.2 wt%. Further, as the rare earth element, for example, misch metal may be contained.

  In addition, according to the present invention, there is provided a Zn alloy die-cast product, which is manufactured by a die casting method using these Zn alloys for die casting.

  ADVANTAGE OF THE INVENTION According to this invention, the Zn alloy for die castings excellent in the fluidity | liquidity (molten metal flow property) of the molten metal at the time of die-casting can be provided. A Zn alloy die-cast product manufactured using the die-casting Zn alloy of the present invention has significantly reduced void defects, reduced surface defects and blister defects, and improved mechanical properties such as strength, elongation, and Young's modulus. For this reason, productivity is improved, the yield is improved, and the wall thickness can be reduced more than the conventional product. Therefore, the product can be reduced in weight.

The significance of each composition component in the Zn alloy for die casting of the present invention is as follows.
Al improves the fluidity of the molten metal during die casting. However, Zn alloy for die casting is an alloy that can be hot chambered, and if the Al content increases, the melting point becomes high and the hot chamber may become difficult, so the added amount of Al is 3 to 5 wt%. preferable.

  Mg is contained in order to suppress intergranular corrosion. When the content is small, the suppression effect is low, but when the content is large, the impact strength of the Zn alloy die-cast product may be lowered. Therefore, the addition amount is preferably 0.03 to 0.06 wt%.

  By adding Cu, the strength can be further improved. However, if the addition amount increases, the fluidity and impact strength may be lowered. Therefore, when Cu is added, the addition amount is in the range of 0.5 to 5 wt%.

  Rare earth elements are 15 elements from La to Lu, and by adding one or more of these rare earth elements, the occurrence of “nest” which is a cavity defect is suppressed, and the mechanical properties of Zn alloy die cast products Can be improved. As the rare earth element, for example, misch metal is preferably added.

  The rare earth element content is preferably 0.01 to 1.0 wt%, and the rare earth element content is preferably less than 0.2 wt%. For example, when adding two or more rare earth elements as in the case of adding misch metal, the total content of these two or more rare earth elements (eg, misch metal) is 0.01 to 1.0 wt%. More preferably, the total content of the two or more rare earth elements (for example, misch metal) is less than 0.2 wt%. Furthermore, if the total content of these two or more rare earth elements (for example, misch metal) is set to a low content of 0.01 to 0.15 wt%, the hot metal flowability is improved as well as the cavity defect reduction effect. It is. When the content of the rare earth element is 0.2 wt% or more, the melting time for producing an alloy ingot used for die casting becomes long, which is not economical. When the rare earth element content exceeds 1.0 wt%, such disadvantages become more prominent.

  In the case of adding a rare earth element, Al and a rare earth element may be included in the die casting Zn alloy by adding a mother alloy composed of, for example, a rare earth element such as misch metal: about 10 wt% and Al: about 90 wt%. .

  Thus, the Zn alloy for die casting of the present invention containing a rare earth element is excellent in the fluidity (molten metal flow) of the molten metal during die casting, and can suppress the generation of hot water wrinkles and the like. In the Zn alloy die-cast product of the present invention manufactured using this die-casting Zn alloy, the cavity defects are remarkably reduced, the surface defects and the blister defects are reduced, and the mechanical properties such as strength, elongation, and Young's modulus are reduced. The characteristics are also improved. For this reason, productivity is improved, the yield is improved, and the wall thickness can be reduced more than the conventional product. Therefore, the product can be reduced in weight. The Zn alloy die-cast product of the present invention is suitably used for, for example, automobile-related parts, machine parts, building hardware, ornaments and the like.

  Add electric Zn, predetermined amount of Al and Mg, and if necessary Cu to the graphite crucible, and further add a master alloy (rare earth element Al alloy) consisting of misch metal: about 10 wt% and Al: about 90 wt% Then, after being melted at 600 ° C., it was cast into a mold preheated to 150 ° C. at a molten metal temperature of 450 ° C., and a Zn alloy for die casting containing rare earth elements as Comparative Examples 3 to 5 and Example 1 of the present invention. Each alloy ingot was prepared. Further, Comparative Examples 1 and 2 as Zn alloys for die casting not containing rare earth elements in the same manner except that a mother alloy (rare earth element Al alloy) comprising misch metal: about 10 wt% and Al: about 90 wt% is not added. Each alloy ingot was prepared. Table 1 shows the composition of each component in the die casting Zn alloys of Example 1 and Comparative Examples 1 to 5.

(Flow length measurement)
Each ingot of Comparative Example 3 and Comparative Examples 1 and 2 was dissolved, and the flow length of the solution at 410 to 460 ° C. was measured. An MIT fluidity tester was used for the measurement. The conditions of the MIT test apparatus are: vacuum pump differential pressure set value: 100 Torr, suction Pyrex tube (“Pyrex” is a registered trademark): inner diameter φ5 mm, outer diameter φ7 mm (L-shaped tube), number of tests: one / time . The measurement results are shown in Table 2 and FIG. In Comparative Example 3, although the flow length is shorter than that in Comparative Example 1, it can be seen that it is superior to Comparative Example 2. In the comparative example 1, during an actual die casting operation, an appropriate temperature is 410 ° C. to 420 ° C., which corresponds to a flow length of 200 to 300 mm. On the other hand, the temperature range of Comparative Example 3 is 410 ° C. to 430 ° C., and the same flow length as that of Comparative Example 1 is secured, and it is considered that the die casting temperature range during operation can be taken gently.

  Next, using these alloy ingots of Example 1 and Comparative Examples 1 to 5, the length for investigating the characteristics of the Zn alloy die cast product by hot chamber die casting under the conditions of a molten metal temperature of 420 ° C. and a mold temperature of 150 ° C. A tensile test piece having a parallel part length of 30 mm, a parallel part diameter of φ7 mm, and a handle part of φ10 mm and a plate-like test plate piece of 50 mm × 70 mm × 3 mm were prepared. And each test was done using these tensile test pieces and test plate pieces. Hereinafter, the characteristics of the present invention will be described by comparing Example 1 and Comparative Examples 1 to 5.

(Differential thermal analysis)
Differential thermal analysis was performed on each alloy ingot of Example 1 and Comparative Examples 1-5. As a result, in the comparison between Comparative Examples 3 to 5 and Comparative Example 1, the misch metal content is particularly in the range of 0.05 to 0.10 wt%, and in the comparison between Example 1 and Comparative Example 2, When the content of misch metal was 0.02 wt%, the solidus temperature (solidification end temperature) was lowered. This is thought to be related to the improvement of the hot water flow property during die casting.

(Hardness test)
The cross-sectional hardness of the test plate pieces of Comparative Examples 3 to 5 and Comparative Example 1 was measured using a micro Vickers hardness meter. The test load was 200 g × 10 s. As a result, FIG. 2 was obtained. It has been found that the hardness increases as the content of misch metal increases.

(Cross section observation)
The cross sections of the test plate pieces of Comparative Examples 3 to 5 and Comparative Example 1 were photographed and subjected to image analysis. The images of Comparative Examples 3 to 5 and Comparative Example 1 are shown in FIGS. Using Image-Pro Plus as the image analysis software, the area ratio of the shrinkage nest part and the area ratio of the good part (the part without the shrinkage nest) were calculated, and the results were as shown in Table 3. By adding misch metal, the shrinkage nest area was reduced by about 50 to 80%.

(Tensile test)
The tensile test pieces of Comparative Example 3, Example 1 and Comparative Examples 1 and 2 were each subjected to a tensile test with an Instron type tensile tester under the test conditions of a tensile speed of 10 mm / min. The amount of displacement (elongation) until failure was measured. About the tensile test piece of the comparative example 3 and Example 1, the tensile fracture strength and elongation were similarly measured about the thing after annealing. As a result, FIGS. It was found that in both Comparative Example 3 and Example 1, the tensile strength was increased by 20 to 30% and the elongation was increased by 40 to 60% compared to the case where no misch metal was contained. Further, it was found that, when annealed, the tensile strength was reduced by about 10% compared to before annealing, but the elongation was further increased by 20-30%. It has been found that the Young's modulus tends to increase as the misch metal content increases.

(Fracture surface observation)
The fracture surfaces of the tensile test pieces of Comparative Example 3, Example 1, and Comparative Examples 1 and 2 that were broken by the tensile test were observed. Photographs of each fracture surface are shown in FIGS. As a result, it was seen that the tensile test pieces of Comparative Examples 1 and 2 that did not contain misch metal were broken starting from the shrinkage nest. On the other hand, it is considered that Comparative Example 3 and Example 1 do not have a large shrinkage nest, thereby increasing tensile strength and elongation.

  Next, an alloy ingot of Comparative Example 6 was prepared as a die casting Zn alloy containing Al: 4 wt%, Mg: 0.04 wt%, Misch metal: 0.2 wt%, and the balance consisting of Zn and inevitable impurities. . However, in order to reduce the loss rate when adding the misch metal to 10% or less, the melting time when producing the alloy ingot of Comparative Example 6 is the same as that of Comparative Example 4 (Al: 4 wt%, Mg: It took 0.02 wt%, misch metal: 0.1 wt%, and the time required for the dissolution was approximately twice as long as that for the production of a die casting Zn alloy consisting of Zn and inevitable impurities. In addition, in order to make it the same as the melt | dissolution time at the time of manufacturing the alloy ingot of the comparative example 4 about the comparative example 6, it is necessary to strengthen stirring power, but then, the loss rate at the time of misch metal addition will be 60%. (The blending value is about 0.5 wt% misch metal), which is not economical.

It is a graph which shows the result of the flow length measurement of a solution. It is a graph which shows the result of a hardness test. 4 is a photograph of a cross section of a test plate piece of Comparative Example 1. 10 is a photograph of a cross section of a test plate piece of Comparative Example 3. 6 is a photograph of a cross section of a test plate piece of Comparative Example 4. 10 is a photograph of a cross section of a test plate piece of Comparative Example 5. It is a graph which shows the tensile fracture strength in a tension test. It is a graph which shows the displacement amount (elongation) in a tension test. 3 is a photograph of a fracture surface of Comparative Example 1. 10 is a photograph of a fracture surface of Comparative Example 3. 10 is a photograph of a fracture surface of Comparative Example 2. 2 is a photograph of a fracture surface of Example 1 taken.

Claims (4)

  Al: 3 to 5 wt%, Mg: 0.03 to 0.06 wt%, Cu: 0.5 to 5 wt%, one or more rare earth elements: 0.01 to 1.0 wt%, the balance being A Zn alloy for die casting, characterized by comprising Zn and inevitable impurities. 2. The Zn alloy for die casting according to claim 1, wherein the rare earth element content is less than 0.2 wt%.   The Zn alloy for die casting according to claim 1 or 2, wherein a misch metal is contained as the rare earth element. A Zn alloy die-cast product manufactured by a die-casting method using the Zn alloy for die casting according to claim 1, 2 or 3.