JP3405602B2 - Manufacturing method of aluminum alloy drill screw - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum alloy drill screw, and more particularly to a method for manufacturing an aluminum alloy drilling tapping screw which is lightweight and has excellent corrosion resistance and durability.

[0002]

2. Description of the Related Art Conventionally, various mechanical devices, vehicles and the like have been usually manufactured mainly by using steel materials. However, in recent years, there is a tendency to demand weight reduction in order to increase the operating speed and save energy. For example, light metal materials such as aluminum, titanium, and magnesium, ceramic materials, reinforced plastics, or composite materials of these, etc. It is being manufactured with a material having a small specific gravity.

On the other hand, the bolts are manufactured by using a steel material which has a large tensile strength and is relatively easy to work, but it has a disadvantage in handling because of its large specific gravity. Further, even when main members such as mechanical devices are made of a material having a low specific gravity, bolts for connecting them are neglected because of their small size, and those made of steel are often used as they are. However, when the number of bolts used is large, it cannot be ignored in terms of reducing the overall weight, and there is also a problem that corrosion deterioration is likely to proceed when the light metal material and the steel material come into contact with each other.

[0004]

Therefore, attempts have been made to manufacture bolts from a light metal material such as aluminum, and the standard for aluminum alloy bolts (JI
S-B-1057) has also been enacted, but most tapping screws, especially drill screws with a drill formed at the tip, are made of iron-based alloys and have strength and durability. Moreover, tapping screws made of light metal, which have the same economic efficiency as screws made of steel, have not yet been obtained.

Therefore, the present invention is intended to provide a tapping screw made of an aluminum alloy which is lightweight and has practical strength, and which is also economically satisfactory, and has corrosion resistance without impairing the strength of the screw. It is an object of the present invention to provide a method for producing an aluminum alloy drill screw having practical drilling performance and tapping performance by significantly improving the surface hardness and surface hardness.

[0006]

The object of the present invention is as follows.
A first step of forming a nickel-phosphorus alloy coating with a film thickness of 5 to 50 μm by plating a drill screw formed of a 7000 series or 2000 series aluminum alloy in a reducing phosphorus compound-containing nickel plating bath, and a non-oxidizing property. 45 in the atmosphere
The second step of quenching from a temperature above 0 ° C and 2 in vacuum
This can be achieved by a method for manufacturing a drill screw made of an aluminum alloy, which comprises sequentially performing a third step of aging treatment at a temperature of 50 ° C. or lower.

The 7000 series or 2000 series aluminum alloy wire for forming a screw for applying the method for manufacturing an aluminum alloy drill screw of the present invention is not particularly limited, but a 7050 series aluminum alloy wire is preferably used. To be

A method such as forging is used to manufacture a screw using such an aluminum alloy wire rod. For example, the head portion is compressed in the axial direction to increase the diameter, and the screw portion is compressed in the radial direction. Then, it is formed so as to make a screw thread. At this time, it is preferable to set the processing conditions such that the processing degrees of all parts are within the range of 0.35 to 0.8 in terms of natural logarithm of processing strain. If there is a portion where the value of the workability is less than 0.35, the crystal grain size becomes coarse in the heat treatment of the next step and it is easy to break during use. Therefore, the workability is further increased to 0.35 or more. To do. When the value of the workability exceeds 0.8, there is no problem of strength reduction after heat treatment, but work cracking is likely to occur during forging, so work of 0.8 or more is not preferable.

The screw forged from the aluminum alloy wire rod as described above is, as a first step, an electroless plating method using an electroless nickel plating bath containing a hypophosphorous acid compound or an electrolytic method containing a phosphoric acid compound. A nickel-phosphorus alloy coating is formed on the surface of the nickel plating bath by an electrolytic plating method or the like. Further, by suspending hard ceramic powder such as alumina, silicon carbide, silicon nitride, or boron nitride in a nickel plating bath, these ceramic powders can be dispersed and co-deposited in the nickel-phosphorus alloy coating film. This makes it possible to obtain a screw having more excellent surface characteristics. The thickness of the nickel-phosphorus alloy coating is preferably in the range of 5 to 50 μm.

Next, the thus-plated screw is subjected to a solution treatment of heating it to 450 ° C. or higher and then rapidly cooling it to, for example, 120 ° C. or lower, which is carried out in a non-oxidizing atmosphere as a second step. It As the non-oxidizing atmosphere, for example, a mixed gas of carbon dioxide, carbon monoxide, nitrogen or the like can be used. By this solution treatment, the distortion of the crystal structure inside the material disturbed by the forging of the screw is relaxed, and the structure is adjusted as a preparatory step of the aging treatment to be performed later, but at the same time, it occurs during electroless plating. Then, the hydrogen stored in the tissue is also released.

In the third step, the solution-solubilized screw is subjected to a temperature of 250 ° C. or lower, for example, 120 to 220.
The aging treatment is carried out at a temperature of 50 ° C. for a total of 50 to 60 hours, and it is desirable to select the optimum combination of the temperature and time conditions depending on the purpose. In the present invention, this treatment is carried out in a vacuum atmosphere. As a result of such treatment in a vacuum, the distribution of precipitates that contribute to the strengthening of the crystal structure inside the material is controlled and the grain boundaries are also strengthened. Further, the tensile strength of the screw is improved, the surface hardness and the stress corrosion resistance are strengthened, and further, the desorption of hydrogen remaining without being released in the second step also progresses and the toughness is increased.

[0012]

According to the method for manufacturing a drill screw made of an aluminum alloy of the present invention, corrosion resistance and surface hardness can be obtained without particularly complicating the screw manufacturing process and without impairing the strength and toughness of the screw formed by forging. Can be increased.

[0013]

EXAMPLE A 7050 aluminum alloy wire rod having a diameter of 6 mm was used, and the natural logarithmic value of working strain was 0.
The head was set up so that it was within the range of 35 to 0.8, and the screw part was extruded to forge to form a drilling tapping screw having a nominal diameter of 4.8 mm and a pitch of 1.6 mm. Next, the screw was subjected to electroless plating of a nickel-phosphorus alloy film having a thickness of about 25 μm using an electroless nickel plating bath containing a hypophosphorous acid compound (Nihon Kanigen, Sumer K-102).

A screw which has been subjected to the treatment of the first step is
A heat treatment was carried out at 480 ° C. in a non-oxidizing gas atmosphere consisting of carbon dioxide, carbon monoxide, and nitrogen, and then rapidly cooled to carry out the second step treatment which also serves as solution treatment and dehydrogenation. Furthermore, after holding at 120 ° C for 24 hours in a vacuum of 1 Torr or less, it is heated for a short time so that the temperature does not reach 250 ° C once to re-dissolve the intermetallic compound preferentially precipitated at the grain boundary of the matrix phase, and then to 170 ° C. The aging treatment which is the third step was performed while changing the temperature stepwise from 1 to 120 ° C. to obtain the aluminum alloy drill screw A of the present invention. This screw A is JIS
-B1057-AL6 was satisfied with the mechanical properties, and it had sufficient strength to open a screw hole in a steel frame formed of a steel plate having a thickness of 3.2 mm.

Further, fine powder of silicon carbide is suspended in an electrolytic nickel plating bath to which a phosphoric acid compound is added and co-deposited on the electrodeposition film, and the thickness of the fine powder of silicon carbide dispersed and contained is about 1. An aluminum alloy drill screw B of the present invention was obtained by the same procedure as described above except that a nickel-phosphorus alloy film having a thickness of 20 μm was formed. This screw B is the above-mentioned screw A
In addition to having the same mechanical properties as above, it had higher surface strength.

[0016]

According to the method for manufacturing a drill screw made of an aluminum alloy of the present invention, it is lightweight, has sufficient surface hardness and toughness for drilling a screw hole in a steel plate, and has a large tightening strength. Therefore, it is possible to economically produce a drill screw made of an aluminum alloy having excellent corrosion resistance and high reliability.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-5-71525 (JP, A) JP-A-63-166955 (JP, A) JP-A-57-137459 (JP, A) JP-A-60- 197880 (JP, A) JP-A-3-47655 (JP, A) JP-A-6-240437 (JP, A) JP-A-6-346220 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 18/36 C22F 1/053 C23C 18/52 F16B 33/06 C23C 18/31

Claims (2)

(57) [Claims] 1. A first step for forming a nickel-phosphorus alloy coating having a thickness of 5 to 50 μm by plating a drill screw formed of a 7000 series or 2000 series aluminum alloy in a nickel plating bath containing a reducing phosphorus compound. And an aluminum alloy drill characterized by sequentially carrying out a second step of quenching from a temperature exceeding 450 ° C. in a non-oxidizing atmosphere and a third step of aging treatment at a temperature of 250 ° C. or less in a vacuum. Screw manufacturing method. 2. The method for producing an aluminum alloy drill screw according to claim 1, wherein a nickel-phosphorus alloy coating film in which the ceramic powder is dispersed and co-deposited is formed using a nickel plating bath in which hard ceramic powder is suspended.