JPS619597A - Plating method of aluminum piston - Google Patents

Abstract

PURPOSE:To give wear resistance and baking resistance to a piston made of aluminum by performing alkali etching treatment and zinc-substituting treatment to the base material for a piston made of aluminum, thereafter subjecting the base material to the electroless plating of nickel and copper and plating iron- base metal thereon. CONSTITUTION:After the base material for a piston made of aluminum alloy is immersed into aq. soln. of sodium hydroxide or the like to perform alkali etching, it is washed with water and pickled. Then, it is immersed into a treating soln. contg. sodium hydroxide or the like and zinc oxide to perform zinc-substituting treatment. Successively, after performing the electroless plating of nickel or copper, the prescribed iron-base metal plating can be uniformly performed without an auxiliary electrode and the iron-base metal-plated piston made of aluminum which is excellent in strength of wear resistance and baking resistance or the like is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a plating method for iron-based metal plating, which is applied for the purpose of imparting wear resistance and seizure resistance to all-aluminum engine pistons. (Conventional technology) In an all-aluminum engine in which both the cylinder liner and piston are made of aluminum, the piston surface must be plated with good wear resistance and seizure resistance.
Iron-based plating is generally used as a plating with good wear resistance, but iron plating baths have a pH value of 1 to 2.
Therefore, if an aluminum piston is directly immersed in a plating bath, the aluminum material and the zinc in the zinc substitution layer applied as a base treatment for plating will be eluted, resulting in problems such as poor plating adhesion.

In order to prevent such problems from occurring, it is common practice to apply base plating to the aluminum piston in a plating bath with a high pH value before applying iron-based plating. ↓) Copper or nickel was plated to a thickness of about 3 to 5 μm by electroplating in a copper cyanide bath, a nickel sulfur amino acid bath, etc. with a pH of 4 to 6. It is commonly used for plating,
Although it has the advantage of being able to plate thickly, there is a problem that the plating coverage is poor unless the appropriate electrode is selected according to the shape of the object to be plated. Therefore, an auxiliary anode is used for plating the inside of the piston. must, etc.
The problem was that the plating process was complicated. If this plating is insufficient, it naturally causes problems in the subsequent plating of iron-based metals. Therefore, there has been a need for a method of plating aluminum pistons that is easier to operate than conventional methods and that allows subsequent ferrous metal plating to be performed without any problems.

(One problem to be solved by the invention) The present invention responds to the above-mentioned conventional demands, and does not require auxiliary electrodes etc. during base plating, and can uniformly plate copper or nickel. It is an object of the present invention to provide a method for plating aluminum pistons with a good metal plating finish. We solved the above problems by using electroless plating, which has not been previously used as a base treatment for iron-based plating on aluminum pistons, because plating has problems with adhesion and is expensive. ◎ That is, the method of plating an aluminum piston of the present invention involves performing a base treatment such as alkali etching on an aluminum piston base material, performing a zinc substitution treatment, and then plating with nickel or copper by electroless plating, and then plating with a specified iron. ◎ The aluminum piston base material to be plated in the present invention is not particularly limited, and conventional piston base materials can be used. If so, after physical polishing such as sandblasting, degreasing with K such as Triclean ultrasonic cleaning, followed by alkaline etching, pickling, and zinc replacement treatment. It may be performed more than once, for example twice. In each treatment step, electroless plating (chemical plating) is performed after zero zinc replacement treatment, which is preferably performed with sufficient water washing. After electroless plating, wash with water and perform conventional iron plating, iron-phosphorus alloy plating, or composite plating using these as a base bath using electrolytic plating K.Finally, tin plating is performed using electrolytic plating K to achieve the desired purpose. Obtaining an aluminum piston0 In the present invention, iron plating means plating of an iron-based alloy that has strength such as wear resistance and seizure resistance〇〇
Effect] In the present invention, the zinc substitution treatment is carried out to improve the adhesion of plating, especially copper or nickel plating.

In the present invention, as in the conventional method, NaOH and Zn
This is done by immersion in an aqueous solution containing O.

The electroless plating performed in the present invention is to prevent the aluminum piston from being corroded by the plating bath during the next iron plating, and therefore the piston surface is uniformly coated to the extent that the purpose of corrosion prevention is achieved. As the zero plating bath for plating, a copper plating bath or a nickel plating bath for normal electroless plating can be used.The amount of plating is about 1 to 3 μml, usually about 2 μm.

Plating with iron-based metal is performed in order to impart wear resistance and seizure resistance to the piston. Plating with ◎ is performed in exactly the same way as conventional aluminum piston plating. The final tin plating is done to improve the initial conformability of the piston and to prevent corrosion of the iron plating. Usually, iron plating is about 20μm,
The tin plate is plated to a thickness of about 1 to 2 μm.

(Example and comparative example) The present invention will be explained below with reference to Examples and Test Examples.

Embodiment The plating process will be explained according to FIG. 0, which is a process diagram showing one embodiment of the present invention. The aluminum piston base material to be plated is aluminum alloy ('AC8A, T
6) was used.

1. Ultrasonic cleaning in degreasing trichlene.〇 Dive for 60 seconds in an aqueous solution of 10% sodium hydroxide at a 50°C alkali etching solution temperature. After washing with water, perform the next process (all items are washed with water before moving on to the next step).

120 t/l NH4HF in HNO3 aqueous solution
Immerse for 50 seconds in a treatment solution containing ◇The solution temperature is room temperature (unless otherwise specified, the solution temperature indicates room temperature) Immerse for 60 seconds in a treatment solution containing 500t/l of zinc-substituted NaOH and 100t/l of Zn Process〇 & Pickling Immerse in 50% HNO3 aqueous solution for 30 seconds.

& Zinc replacement Treated in the same manner as above ◇ l Electroless nickel plating Electroless plating was carried out using a commercially available electroless Ni plating solution, trade name Nimuden 5× (manufactured by Uezai Kogyo ■).

Film thickness: 2μllt.

a Iron plating or iron phosphorus plating Plating was carried out to a thickness of approximately 20 μm using each of the following plating baths.

1) Iron plating bath composition: FeC4500? /1 CaC1,340t/l pH1,0-1.5 Bath temperature: 90℃ Plating conditions: Current density 6A/(h? time
20 minutes 2) Iron, phosphorus plating bath composition: Fe3O4, 7H20250f/LNH4C
t50? /1H3B0.
20t/1N) 14F, HF 5
t/1At2(804)3.14~18H201f/
1NaH2PO2, H2Oα1 t/l pH 1,6-2.0 Bath temperature: 60°C Plating conditions: Current density 4A/dm” Time 2
0 minute ρ tin plating Electrolytic plating was carried out to a film thickness of 1 μm using a commercially available tin plating bath 5N-252 manufactured by Dipsol ■.

Iron plated aluminum piston and iron by the above plating process,
Two types of phosphor-plated aluminum pistons were obtained.

Comparative Example In the above plating process, the 7th electroless plating was replaced with the conventional electrolytic plating, and the same process was used to produce iron-plated aluminum pistons and iron.

Two types of phosphor-plated aluminum pistons were obtained. The electrolytic nickel plating conditions were as follows.The plating film thickness was 5 μm on the piston surface.Bath Composition Nisluamic acid N
i 4609/L Nickel chloride 12 t/
l Boric acid 45 f/l pH 4.0 to 4.4 Bath temperature: 50°C Plating conditions: Electrolyte density 4 A/d 1 hour 5 minutes Test example 1 Four types of aluminum pistons obtained in the above examples and reference examples were Each is attached to a 4-cylinder, 2000cc engine,
When a 100-hour bench test was conducted, there were no problems at all.

Test Example 2 In the plating treatment of the example, the electroless nickel plating was plated in four stages of film thickness Q, 5 μFK, 1 μm, 3 μm, and 5 μm.
Four types of iron-plated aluminum pistons for CC were manufactured.

Similarly, in the plating process of the above comparative example, the film thickness of the electrolytic nickel plating was 1 μm and 5 μm on the piston surface.
Four types of iron-plated aluminum pistons were produced in the same manner except that the thickness was changed to four stages: , 5 μm, and 7 μm.

Visually judging the finished condition of each of the above four types of iron-plated pistons, we found that those with electrolytic nickel plating with a plating film thickness of 1 μm and 3 μm have iron plating on the parts where nickel does not spread well during iron plating. It was found to be in a state of being contaminated by the bath, and was judged to be unusable.

As for those with residual residue, when they were assembled into an engine and subjected to an engine bench test for 100 hours, some peeling of the iron plating was observed on those electrolessly plated with a Ni plating thickness of 0.5 μm. Furthermore, in the case of the electroless Ni plating with a thickness of 5 μm, cracks were observed in the iron plating when a dent was made on the piston surface after the test.

On the other hand, those with electrolytic Ni plating have a Ni plating thickness of 1 μm.
Good results were obtained in all cases except for those with a diameter of 3 μm.

From the above test results, it can be seen that electrolytic Ni plating requires a plating thickness of 4 μm or more at least on the surface due to the throwing power. On the other hand, electroless Ni plating is 0.
Peeling of the iron plating was observed at 5 μm, and cracking was observed in the iron plating at 5 μm, so the plating film thickness was 1 to 4 μm.
It can be seen that it is necessary to be within the range of m. The above results can be obtained in the case of copper plating as well.

(Effect) The present invention uses electroless plating as the base plating for iron plating on aluminum pistons, and due to its effectiveness, there is no need to use auxiliary electrodes as in the past, simplifying the plating process. ◇Furthermore, since the thickness of the base plating of the present invention is smaller than that of conventional electroplating, it has various excellent effects, including economical advantages.◇

[Brief explanation of the drawing]

The figure shows a process diagram of an embodiment of the present invention. Patent applicant: Toyota Motor Corporation Same Uemura Kogyo Co., Ltd.

Claims (1)

[Claims] It is characterized by subjecting the aluminum piston base material to preliminary treatment such as alkali etching, followed by zinc substitution treatment, and then applying 1 to 4 μm of nickel or copper plating by electroless plating, and then applying a predetermined iron-based metal plating. Aluminum piston plating method.