JPH0210215B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum alloy material for a laser reflecting mirror and a method for manufacturing the same. Laser reflectors are used as important functional parts in computer data input/output devices (laser printer optical disk devices, etc.), automatic price reading devices (POS), digital audio disks (DAD), and surface inspection devices. The materials used include aluminum alloy, copper, brass, and glass, but all of them are used after processing the surface of the material to make it smooth and then subjecting it to a surface treatment that has a high reflectance to the laser. To be used as a laser mirror, the final reflectance of the laser beam must be 90% or more, and for this reason, the material must have the best possible flatness and surface roughness. A rotating polygon mirror is required to have mechanical strength that can withstand high-speed rotation. When aluminum alloy is used as the material for this laser mirror, conventionally the material is first plane-machined using a precision grinder or precision cutting lathe, then electroless nickel plating is applied to the surface of the material, and finally wrapping is performed. I came. However, this method requires a complicated process to form a glossy nickel plating layer on the surface of the material and the wrapping process takes a very long time, resulting in high costs.Also, since the process involves multiple steps, the surface may be scratched. The number of occurrences has increased, and this has been a cause of lower product yields. To avoid these problems, there is a method of cutting aluminum alloy material with ultra-precision cutting using a diamond cutting tool and then applying surface protection treatment to produce the product.This significantly reduces processing costs. . However, in this method, the surface of the machined aluminum alloy material is used as a reflection surface for the laser beam, so the material itself is required to have advanced characteristics regarding the laser reflection function, and the plating and wrapping processes are difficult. It is difficult to satisfy these required characteristics with the aluminum alloy materials used in the conventional combination method. The aluminum alloy material used in the manufacturing method of laser mirrors, which combines ultra-precision cutting with a diamond cutting tool and surface protection treatment, is generally required to have the following properties. (1) Excellent cutting performance with a diamond cutting tool. In other words, the amount of elastic deformation in response to compressive stress at the cutting edge is small, and a process-affected layer is difficult to form. Also, there should be no traces of the cutting edge left on the machined surface. (2) The surface roughness of the machined surface is small, and Rmax is
Must be 0.02μm or less. As a result, steps and inclusions at grain boundaries may remain on the machined surface,
Also, the cut by the cutting edge must not remain in the form of a recess. (3) The machined surface must have good flatness. In particular, for rotating polygon mirrors that use flat side surfaces as reflective mirror surfaces, it is desirable that the parallelism of the upper and lower surfaces be 1 μm or less, and the material must be difficult to retain machining distortion. (4) The reflectance for laser light should be as high as possible. The processed surface of the material must have a reflectance of at least 87% or more, preferably 90% or more. (5) 20,000 to 8 per minute as a material for rotating polygon mirrors
It must have sufficient rigidity and strength so that the laser light reflection function will not deteriorate due to surface vibration, elastic deformation, or plastic deformation during high-speed rotation of 10,000 rotations. The inventors of the present invention have conducted various studies on aluminum alloy materials that can satisfy these required properties, and have found that they have excellent machinability with a diamond cutting tool, minimize inclusions and crystallized substances, and optimize crystal grain size. We have successfully developed an aluminum alloy for laser mirrors that has a reflectance of around 90% or more and has sufficient mechanical strength even for high-speed rotation by adjusting the reflectance, and a method for manufacturing the same. The content of the invention will be described in detail below. In order to obtain good surface properties as shown in the above-mentioned required property (2), coarse intermetallic compound particles and nonmetallic inclusion particles should be prevented from existing in the material as much as possible. If these particles are present, they will remain as protrusions on the surface after cutting, or the marks left by the cutting will remain on the surface as hole-like depressions, causing laser light scattering in these areas. To deal with these problems, it is necessary (i) to remove nonmetallic inclusions by filtering the molten aluminum alloy using a filter medium with a pore size of 10 μm or less, and (ii) to remove insoluble intermetallic compound particles. In order to suppress the amount of formation as much as possible, the amount of elements that form insoluble intermetallic compounds must be limited. In other words, the iron contained as an impurity in the alloy is 0.05% or less,
Titanium must be kept below 0.02%, and manganese and chromium each below 0.03%. Regarding silicon, a coarse compound Mg ₂ Si is formed with magnesium, which is a blended element, during annealing of the alloy, which causes unevenness on the surface during cutting, so it is desirable to limit the content to 0.05% or less. In order to obtain a reflectance of around 90% or higher as described in (4), it is necessary to suppress the formation of non-metallic inclusions and intermetallic compounds as much as possible as described above, but also to prevent the formation of non-metallic inclusions and intermetallic compounds. The effect can be further ensured by preventing the mirror-like state of the new surface from being deteriorated by chemical changes due to the cutting process. In other words, preservation of the mirror-like state is ultimately achieved by the formation of a surface protective film, but in general, chemical changes on the surface begin immediately after the new surface comes into contact with air during cutting, resulting in slight reflections. A decline in the rate cannot be avoided. The inventors of the present invention have conducted various studies on methods for suppressing such changes, and have found that adding an appropriate amount of beryllium to the material further improves the specular reflectance. In this case, the amount of beryllium added is 0.001
If it is less than 0.0%, the effect will be small, and if it is added at 0.01% or more, no increase in effect can be expected. Therefore, a range of 0.001% to 0.01% is appropriate. Next, we conducted a study to obtain the required characteristics (1), (3), and (5) for diamond cutting tools, such as machining performance, residual stress characteristics, and mechanical strength characteristics such as rigidity against high-speed rotation. Ta. In general, (i) solid solution hardening and (ii) aging (precipitation) effects are widely used as strengthening mechanisms for aluminum alloys. However, although the aging (precipitation) effect of (ii) provides high strength, it is difficult to say that it is an appropriate strengthening method for this purpose, because intermetallic compounds are formed and there is a great risk of coarse particles. Therefore, in the present invention, it was decided to utilize the solid solution effect (i). In other words, by adding 2 to 6% magnesium and further adding 0.02 to 0.25% copper and 0.02 to 0.5% bad lead, or both at the same time, the machine can achieve the required machining performance and rigidity. It was found that the characteristics can be fully satisfied. In this case, if the amount of magnesium added is less than 2%, it is difficult to obtain sufficient strength, and if it exceeds 6%, β-Al ₂ Mg ₃ particles are likely to be generated, and hot workability is significantly deteriorated. causing inconvenience. On the other hand, for copper and zinc, if each is less than the lower limit of 0.02%, sufficient mechanical strength cannot be obtained, and if the upper limits of 0.25% and 0.5% are exceeded, the corrosion resistance of the material will be reduced, so the upper limit of each Should be less than or equal to the value. Magnesium, copper, added as strengthening elements
It is necessary for each of zinc and zinc to be uniformly distributed in solid solution. Therefore, it is effective to heat treat the alloy ingot at a temperature of 400℃ or higher for 2 hours or more and less than 24 hours. be. If the heating temperature is less than 400℃, or if the treatment time is less than 2 hours even if the heating temperature is 400℃ or higher, a uniform solid solution dispersion state of the elements cannot be obtained;
If the temperature exceeds 550°C, or if the heat treatment time exceeds 24 hours even if it is below 550°C, the oxidation of magnesium will become significant, resulting in a decrease in the reflectance of the cut surface, which is inappropriate. Next, the second reason for limiting the above hot working conditions and the following cold working conditions is to limit the crystal grain size in the aluminum alloy material for laser reflecting mirrors.
It is to be 100μm or less. In other words, if the grain size of the material exceeds 100 μm, the grain boundary step on the surface after cutting with a diamond tool becomes significant.
As a result, it becomes difficult to obtain good surface accuracy. These grain boundary steps are closely related to the size of the crystal grains, and at the same time are also strongly influenced by the amount of elastic deformation and residual stress of the material in response to the same compressive stress, and the amount of formed damaged layers. The composition of the aluminum alloy and its heat treatment and processing conditions in the present invention exhibit remarkable effects on these problems. Next, the effects of the present invention will be illustrated by examples. Example 1 Alloys 1 to 14 having the compositions shown in Table 1 were each melted, passed through a filter with a pore size of 10 μm or less, and then cast into a circle with a cross section of 273 mm in diameter using a direct water-cooled semi-continuous casting machine. It was made into a columnar ingot. Of the 14 types of alloys mentioned above, Alloy 1 to Alloy 6 are alloys that fall under the present invention, and Alloy 7 to Alloy 14 are alloys that correspond to the present invention.
The above are comparison alloys.

【table】

[Table] Each of these ingots was heat treated at 480℃ for 12 hours, then hot extruded at 380℃ into a round bar with a diameter of 120mm, and then cold drawn with a cross-section reduction ratio of 43%. A round bar with a diameter of 90 mm was obtained. First, the mechanical properties of the material obtained in this way, such as hardness, tensile strength, yield strength, and elongation, were measured.
Next, the grain size (maximum value) of the crystals was measured. In addition, the surface roughness, the amount of inclusions or crystallized substances, the presence or absence of marks such as cutting edge marks and scratches, and the 60° reflectance of parallel incident visible light on surfaces that have been precision cut using a diamond cutting tool. were measured to evaluate its suitability as a laser reflector. These results are summarized in Table 2, and the alloys according to the present invention all have superior machinability with a diamond bite compared to comparative alloys.
In addition to achieving surface roughness of Rmax0.02μm or less,
Very few inclusions or crystallized substances on the cutting surface, 88%
The excellent suitability of the mirror as a laser reflector was confirmed as the above reflectance was obtained.

【table】

[Table] Example 2 Alloys 2 and 5 according to the present invention used in Example 1 were melted, and various factors such as the presence or absence of filtration with a filter with a pore size of 10 μm or less, hot rolling processing temperature, and cold rolling rate were investigated. The influence of the grain size of the plate and the surface texture of the cut surface by a diamond tool was investigated. In this case, the ingot was heated at 480℃.
The annealing of the cold rolled plate was carried out at 380°C for 1 hour. The results are as shown in Table 3. Materials (material numbers 2-2 and 5-2) manufactured using the invention alloy under the conditions of the invention, i.e. filter treatment, had a hot rolling finish temperature of 400°C or less, and It can be seen that the material manufactured under the conditions of an inter-rolling ratio of 30% or more has excellent properties as a laser reflecting mirror material.

【table】

Claims (1)

[Claims] 1 Contains 2.0 to 6.0% by weight of Mg as an essential element, further contains one or both of Cu 0.02 to 0.25% and Zn 0.02 to 0.5%, and the balance is Al and Consisting of unavoidable impurities, the impurities Mn and Cr are each 0.03% or less, Fe and Si are each 0.05% or less, Ti is 0.02% or less, and the total of impurities other than the above is 0.1% or less. Features aluminum alloy material for laser mirrors. 2 Contains Mg2.0 to 6.0% by weight as an essential element, further contains one or both of Cu0.02 to 0.25% and Zn0.02 to 0.5%, and the remainder consists of Al and inevitable impurities, A molten aluminum alloy containing impurities of 0.03% or less each of Mn and Cr, 0.05% or less each of Fe and Si, and 0.02% or less of Ti, and a total of 0.1% or less of impurities other than the above, is heated to a pore size of 10 μm. After passing through the following filter media, it is cast into a specified ingot, and then this ingot is heat treated at a temperature range of 400 to 550℃ for 2 to 24 hours, and the temperature at the end of hot working is is 400
℃ or less, then cold working to a working degree of 30% or more, and then annealing to reduce the average grain size.
A method for producing an aluminum alloy material for laser mirrors, characterized by making the material 100μm or less. 3 Mg2.0-6.0% by weight as an essential element,
Contains Be0.001~0.01%, further Cu0.02~0.25%,
Contains one or both of Zn0.02 to 0.5%, and the remainder consists of Al and inevitable impurities,
As impurities, Mn and Cr are each 0.03% or less, Fe and Si are each 0.05% or less, and Ti is 0.02%.
% or less, and the total amount of impurities other than those listed above is
An aluminum alloy material for laser mirrors characterized by a content of 0.1% or less.