JPH01290737A - Aluminum alloy for die - Google Patents

Abstract

PURPOSE:To obtain the title Al alloy having high hardness in the direction of plate thickness and having less difference in hardness by rolling or forging an Al alloy ingot having specific compsn. consisting of Zn, Mg, Cu, Zr, Mn, Cr and Al and thereafter subjecting it to solution treatment and aging treat ment. CONSTITUTION:An Al alloy ingot contg., by weight, 5.0-7.5% Zn, 1.0-3.5% Mg, 1.0-3.0% Cu and 0.05-0.3% Zr, regulatively contg. <=0.2% Mn and <=0.15% Cr and the balance Al with inevitable impurities and having <=2mm average grain size is rolled or forged into the prescribed thickness. After that, the plate mate rial is subjected to solution treatment and aging treatment. In an arbitary face of the rolled plate or forged plate obtd. by the above method, the average crystal grain size is regulated to <=1,000mum and the average length of an existing crtystallized compound to <=50mum. By this method, the Al alloy for a die having high hardness in the direction of plate thickness, having less difference in hard ness and having excellent grindability can be obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an aluminum alloy for molds, and in particular, in molds used for molding plastics, rubber, etc.
This invention relates to an aluminum alloy suitable for use in aluminum thick plate members that require strength, machinability, polishability, etc.

(Prior Art and Problems to Be Solved) A mold for molding plastic, rubber, or the like is manufactured by cutting a thick plate into the required mold, and then mirror-finishing or graining the surface.

By the way, when this mold is used for injection molding, for example, the plastic is injected at high temperature and high speed, so it has good abrasion resistance, or the mold surface condition is directly printed on the product surface. Good finish is required. For this reason, the material is required to have characteristics such as high hardness and strength, uniform hardness in the thickness direction, and good polishing workability when achieving a mirror finish.

Conventionally, 7NO1, 7003, and 7075, which are 7000 series alloys, have been used as aluminum alloys for molds.
These alloys have poor hardenability when made into thick plate materials, and the hardness of the plate surface and the center of the plate thickness varies.
Because of the large difference in strength, it has not been possible to fully meet these demands.

In other words, thick plates of 20 a+m or more are usually used for molds, but the above tendency is that as the plate thickness increases,
Since the cooling rate during quenching differs greatly at each location in the plate thickness direction, the difference becomes larger and larger. therefore,
Areas with different hardness will occur within the machined product, and areas with lower hardness will wear more severely, shortening the life of the mold.

In addition, there have been problems such as poor workability, or slight unevenness on the surface during polishing to achieve a mirror finish, which is printed on products such as plastics and loses product value.

An object of the present invention is to eliminate the drawbacks of the above-mentioned prior art, and to provide an aluminum alloy for molds that has a small difference in hardness in the thickness direction and has excellent polishability.

(Means for Solving the Problems) In order to achieve the above object, the present inventors have conducted extensive research from various angles such as the composition and structure of aluminum alloys, and as a result, have appropriately regulated the chemical composition and We have discovered that this is possible by controlling the crystal grain length and the crystallized compound length in the rolled plate or forged plate.

That is, the aluminum alloy for molds according to the present invention has Z
n: 5.0-7.5%, Mg: 1.0-3.5%, Gu
:l, 0 to 3.0% and Zr: 0.05 to 0.3%, Mn: regulated to 0.2% or less and Cr: 0.15% or less, the balance being Al and inevitable impurities. An aluminum alloy consisting of an aluminum alloy ingot having an average crystal grain of 21 or less, which is rolled or forged to a predetermined thickness, and then solution-treated and aged. It is characterized by having a length of 1000 μm or less, an average length of the existing listed compounds of 50 μm or less, high hardness in the thickness direction, and little difference in hardness.

The present invention will be explained in more detail below.

First, the reason for limiting the chemical components in the present invention will be explained.

Zn: Zn is an element that is effective in improving strength and hardness. However, if the content is less than 5.0%, the final product (T6 material)
If it exceeds 7.5%, the amount of crystallized compounds increases, resulting in poor castability and rolling workability, and cracks are likely to occur.

Therefore, the Zn content is in the range of 5.0 to 7.5%.

Mg: Like Zn, Mg is an element that is effective in improving strength and hardness, but if the content is less than 1.0%, the strength and hardness will decrease, and if it exceeds 3.5%, rolling workability will decrease. Therefore, the amount of Mg is 1.0 to 3.
．． The range shall be 5%.

Cu: Like Cu+JZn and Mg, it is an element that is effective in improving strength and hardness, but if the content is less than 1.0%, the strength and hardness will decrease, and if it exceeds 3.0%, the castability will be significantly reduced. make it worse Therefore, the CIJ amount is 1.0-3.0%
The range shall be .

Zr: Zr is an element that is effective in improving the strength of thick plate materials without substantially reducing the hardenability. However, the content is o, o5
If it is less than 0.3%, the hardenability will not be improved, and the hardness and strength at the center of the plate will be insufficient, and there will be no effect. Compounds are generated.

It impairs machinability and polishability. Therefore, the amount of Zr is set in the range of 0.05 to 0.3%.

Cr: Cr is an element that affects strength, hardness improvement, quenching sensitivity, and polishability, and if it is contained more than 0.15%,
In particular, the hardenability of thick plates deteriorates, and the strength or hardness decreases more at the center of the plate thickness than at the plate surface, resulting in poor workability and polishability. Therefore, CrJi is 0.1
Regulated at 5% or less.

Mn: Mn is an element that refines the structure and improves strength, but like Cr, it also affects polishability.

Therefore, the amount of Mn is regulated to 0.2% or less. 0.2%
If it is contained in a larger amount, the polishability in particular deteriorates, which is not preferable.

Although impurities are contained in addition to the above-mentioned elements, the amount thereof is permissible as long as it does not impair the effects of the present invention. For example, T
iS2.1%, Ni≦0.1%, B≦0.001%, B
If e≦0.001% and Na≦0.001%, there is no change in the properties of the mold even if these elements are contained.

Next, the reason for limiting the metal structure of the Al alloy of the above chemical components will be explained.

Molding molds are required not only to have hardness, strength, and machinability, but also to have excellent surface polishability after processing. Therefore, in the present invention, the average crystal grain length and the crystallized compound length are controlled.

That is, if a crystallized compound with an average length of more than 50 μm exists, it will protrude or fall off the surface of the substrate during mirror finishing, creating hole-like defects and significantly impairing polishability.

Furthermore, if the material has a structure with an average grain length of more than 1000 μm, waviness will occur on the surface of the substrate during mirror finishing, which will also impair polishability.

On the other hand, the aluminum alloy material used as the mold has a thickness of about 20 to 200III11, and is often used as a hot-rolled material or as a forged material. For this reason, it is necessary to refine the structure of the Al alloy ingot, and if the average crystal grain of the ingot exceeds 211I+1, subsequent homogenization treatment, hot rolling or forging, and heat treatment (solution treatment 1 aging treatment) etc., it becomes difficult to control the size of crystal grains, resulting in poor polishability. Therefore, the average crystal grain of the Al alloy ingot needs to be 2m11 or less.

Note that the aluminum alloy according to the present invention can be obtained by melting, casting, homogenizing, hot rolling or forging, and heat treating (solution treatment, aging treatment) an alloy having the above composition by a conventional method, but preferred manufacturing conditions After melting and casting, 350 ~
After pre-soaking at 450°C to remove residual stress in the ingot, surface side treatment is performed, and then 400-500°C x 2-48
After time homogenization treatment, hot rolling or forging at 300 to 450°C, then solution treatment and water quenching at 350 to 500°C, 1 to 3% strain relief, 1-wrench, and 120 to b. It is obtained by Of course, the manufacturing conditions are not limited to these and can be changed as appropriate.

Next, examples of the present invention will be shown.

(Example) 50Qmm of alloy with chemical composition shown in Table 1
A thick ingot was homogenized at 450°C for 24 hours, and
Hot rolling was carried out at a temperature of 50 to 300°C to obtain a thick plate material of 60+n thickness.

Next, solution treatment and quenching was performed at 450°C for 60 minutes using a saltpetre furnace, and 1
．． After 5% stretching, 120°C x 24 hours → 150
A two-stage aging treatment of 24 hours at ℃ was performed.

The mechanical properties, hardness, metal structure, polishability, etc. of the obtained material were investigated. The results are shown in Tables 2 and 3.

Note that 1 mechanical properties are determined by 1 of the total plate thickness t, as shown in Figure 1.
A tensile test piece (JIS No. 14A) was cut out in a direction perpendicular to the rolling direction from a portion 72 (indicated by △ in the figure), and evaluated by a tensile test.

As shown in the figure, the hardness is 1/4t of the plate surface and plate thickness.
The Vickers hardness of each part (indicated by ■ in the figure) of 1/2 inch was examined and evaluated.

For the metallographic structure, a sample was taken from a cross section parallel to the rolling surface at a location 1/4 of the plate thickness, polished, and then viewed under a microscope to measure the average length of crystallized compounds and average crystal grain length.

Polishing property was measured by cutting out a sample of 5On+n+mouth in a cross section parallel to the rolling surface from the same area as the metal structure and having a plate thickness of 1/4t, and polishing the sample using the following polishing procedure to give it a mirror finish and finish it with F finish. , surface roughness (Ra, Rmax), waviness of the substrate, protrusion and falling off of the product, etc. were evaluated.

, bisuL [polishing with wind whetstone (#320→#400→#600) ↓ Paper polishing (#1000) ↓ Felt, diamond whetstone (#1800→#300)
0 → #8000) (using compound additive liquid) For the polishing work, fix the sample 1 as shown in Figure 2, and move the polishing tool 2 (grindstone, paper, filter) back and forth as shown by the arrow in the figure. I let him do it.

From Tables 2 and 3, the material of the present invention has, compared to the conventional material,
It has high strength and hardness, and the hardness difference in the thickness direction is small.
Furthermore, it can be seen that the product has excellent polishability, such as surface roughness, low substrate waviness, and little protrusion or falling off of crystallized compounds, and has excellent product properties.

On the other hand, Comparative Example NQ6 lacks strength and hardness;
(17 (equivalent to 7075) has insufficient strength, a large difference in hardness, and poor polishability. Comparative Example N.

No. 8 lacks strength and has a particularly large difference in hardness, resulting in poor polishability. Comparative example No. 9 has high strength and hardness, but
Polishability is poor.

[Blank 1 (Effects of the Invention) As detailed above, according to the present invention, the chemical composition of the A2 alloy is adjusted, and the gold structure (average grain length, product compound) of the rolled material or forged material is It is possible to provide an aluminum alloy for molds that not only has sufficient strength but also has high hardness, small difference in hardness, excellent polishability, and high product characteristics.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing cut-out parts of a tensile test piece and an altitude measurement sample in an example. FIG. 2 is a diagram explaining the polishing procedure. 1... Sample, 2... Polishing tool. Patent applicant Hisashi Nakamura, patent attorney representing Kobe Steel, Ltd. Figure 1 Figure 2

Claims (1)

[Claims] In weight% (hereinafter the same), Zn: 5.0 to 7.5%, M
g: 1.0-3.5%, Cu: 1.0-3.0% and Z
An aluminum alloy containing r: 0.05 to 0.3%, Mn: 0.2% or less and Cr: 0.15% or less, with the balance consisting of Al and inevitable impurities, and the average After rolling or forging the aluminum alloy ingot with crystal grains of 2 mm or less to a predetermined thickness, an average crystal grain length of 1000 μm or less exists on any surface of the rolled plate or forged plate that has been subjected to solution treatment and aging treatment. An aluminum alloy for molds, characterized in that the average length of crystallized compounds is 50 μm or less, high hardness in the thickness direction, and little difference in hardness.