CN104233296A - Method for silvering aluminum and aluminum alloy - Google Patents

Abstract

The invention provides a method for silvering aluminum and aluminum alloy, and belongs to the technical field of metal plating. The method for silvering aluminum and aluminum alloy is achieved by the following technical scheme: (1) carrying out chemical zinc immersion on an aluminum part in a zinc dipping solution, removing surface oxides of the aluminum part, and simultaneously replacing a layer of thin and dense zinc coating; (2) timely transferring the aluminum part after zinc immersion into a cyanide copper plating process, wherein the cuprous cyanide in a cyanide plating solution is high in content, and a work-piece is connected with a cathode of a power supply, carrying out flash plating for 1-2 minutes by using current which is 3-5 times greater than normal current, and then plating for 40-60 minutes at normal current; and (3) silvering after copper plating, electrifying and putting in a slot, impacting for 1-2 minutes by using current of 0.6-1.0A/dm<2>, and reducing the current to 0.3-0.4A/dm<2>. The coating obtained by the method disclosed by the invention is bright and silver in surface, and has fine crystal and uniform appearance.

Description

The method that Al and Alalloy is silver-plated

Technical field

The invention belongs to metal plating technique field, particularly relate to a kind of method that Al and Alalloy is silver-plated.

Background technology

Al and Alalloy is silver-plated, and its degree of difficulty is more silver-plated than copper piece much bigger, and its reason is:

(1) Al and Alalloy has very strong affinity to oxygen, and oxide on surface, once removing, can generate new uneven oxide compound rapidly, affect coating and matrix metal bonding force.

(2) standard potential of aluminium relatively more negative (-1.67V).When alumiaum article immerses containing other metal ion electrolytic solution, can replacement(metathesis)reaction be there is, be loosened, coarse coating.Have a strong impact on coating and matrix metal bonding strength.

(3) aluminium is amphoteric metal, and easy and soda acid reacts, and makes component corrosion, makes plating be difficult to carry out.

Therefore, must take to electroplate different treatment processs from routine, the good coating of bonding force could be obtained on aluminum products.

Summary of the invention

The invention provides a kind of method that Al and Alalloy is silver-plated, adopt the Deposit appearance that the inventive method obtains: surface-brightening silvery white, has careful crystallization and homogeneous outward appearance.

The method that Al and Alalloy of the present invention is silver-plated, is realized by following technical proposals:

(1) alumiaum article carries out chemical zincation in zincate solution, while removing alumiaum article oxide on surface, and the zinc layers that displacement one deck is thin and fine and closely woven;

(2) alumiaum article after soaking zinc should proceed to cyanide electroplating operation in time, and in cyaniding plating solution, cuprous cyanide content is higher, negative electrode of being connected with the mains by workpiece, with 3-5 times flash 1-2min larger than normal current, then under normal current, plates 40-60min;

(3) silver-plated after copper facing, charged lower groove, and with 0.6 ~ 1.0A/dm2, rush of current 1 ~ 2min, then be down to 0.3 ~ 0.4A/dm2.

Embodiment

Below by specific embodiment, the present invention is further illustrated.

1 electroless plated zinc and pre-treatment thereof:

The master operation of chemical zincation has:

Deoil conventional gasoline or clean containing the weak lye of tensio-active agent.

Remove except descaling and remain in piece surface dirt and oxide film, comprise caustic dip and bright dipping

Caustic dip specification

NaOH 50 ~100g/L

Temperature 60 ~ 80 C

Time 0.5 ~ 10.min

Low for surfaceness, the aluminum component that precision is high, should not remove oxide film containing in NaOH weak lye.Work

Specification is:

Na2CO3 20 ~30g/L

Na3PO4 50 ~70g/L

Temperature 70 ~ 80 C

Time 1 ~ 2min

The piece surface of removing oxide film has grey residue, should bright dipping in following solutions:

HNO4 500ml/L

HF 100ml/L

Temperature room temperature

Time 3 ~ 10s

(3) soaking zinc chemical leaching zinc process is in zincate solution, replaces the thin and fine and closely woven zinc layers of one deck, thus prevent oxide film again to generate while removing oxide on surface.Its mechanism is when the aluminum hardware processed is immersed in alkaline zincate, oxide film dissolves, and during AL3O3+2NaOH=2NaAlO2-H2O exposed out purified aluminum surface is heavy by octylate, zinc swaps out, and zinc and aluminium current potential are relatively, it is relatively slower that replacement(metathesis)reaction is carried out, so coating is dense.

Add iron trichloride in zincate solution, make in zinc layers by aluminium displace a small amount of iron, form zinc-iron alloy, its oxidation potential is smaller, is conducive to improving displacement layer and metal level bonding force, and erosion resistance is improved.

First be that Al2O3 dissolves just generation zinc precipitation during first time leaching zinc, therefore zinc-impregnating layer compares rough porous.Its first zinc-impregnating layer need be taken off in 1:1HNO3 and remove.Carry out second time and soak zinc, second time zinc-impregnating layer is even, fine and closely woven, good with basal body binding force, is suitable for aluminum and its alloy treatment before plating.

Chemical zincation liquid technological specification:

Caustic soda 500g/L

Zinc oxide 100g/L

Seignette salt 10g/L

Iron trichloride 1 ~ 2g/L

Temperature 15 ~ 27 C

Time 0.5 ~ 1.0min

Precaution:

Pharmaceutical chemicals used is chemical pure, and technical grade affects qualification rate.

Normal zinc immersion plating layer is Steel Gray or Dark grey, and uniform color is consistent, when occurring piebald, zinc film should be exited in 1:1HNO3 and again processing when color and luster is uneven.

Zinc immersion should use aluminium hanger, because different metal material potential difference is different, has impact to aluminium current potential, causes leaching zinc difficulty, makes contact point out coating decortication.

Note swinging part during leaching zinc, prevent part impact wreckage zinc layers.

2 Al and Alalloy copper facing

2.1 cyanide electroplating

Alumiaum article after leaching zinc should proceed to cyanide electroplating operation in time, for the copper-plated cyaniding plating solution of aluminum component, not containing NaOH and also cuprous cyanide content higher, immersing plating solution for preventing part in an instant causes zinc film to dissolve and copper contact precipitation, workpiece should to be connected with the mains negative electrode, with 3-5 times flash 1-2min larger than normal current, then under normal current, plate 40-60min.

Technological specification is as follows:

Copper hydroxide 60 ~ 70g/L

Sodium cyanide 20 ~ 25g/L

Sodium carbonate 30 ~ 50g/L

Seignette salt 60g/L

Sodium Thiocyanate 99 3 ~ 8g/L

Dk 0.4 ~0.6A/dm

t 40~55

3 Al and Alalloy are silver-plated

Silver-plated after copper facing, silver-colored current potential comparatively copper just, should prevent replacement(metathesis)reaction, notes charged lower groove, and with 0.6 ~ 1.0A/dm2, rush of current 1 ~ 2min, then be down to 0.3 ~ 0.4A/dm2

Technological specification

Silver chloride 25 ~ 35g/L

Potassium cyanide (dissociating) 35 ~ 45g/L

Salt of wormwood 30 ~ 80g/L

Dh 0.3~0.4A/dm2

T room temperature

Sedimentation speed 10 ~ 12.

Claims (1)

1. the method that Al and Alalloy is silver-plated, is characterized in that comprising the following steps:

(1) alumiaum article carries out chemical zincation in zincate solution, while removing alumiaum article oxide on surface, and the zinc layers that displacement one deck is thin and fine and closely woven;

(2) alumiaum article after soaking zinc should proceed to cyanide electroplating operation in time, and in cyaniding plating solution, cuprous cyanide content is higher, negative electrode of being connected with the mains by workpiece, with 3-5 times flash 1-2min larger than normal current, then under normal current, plates 40-60min;

(3) silver-plated after copper facing, charged lower groove, and with 0.6 ~ 1.0A/dm2, rush of current 1 ~ 2min, then be down to 0.3 ~ 0.4A/dm2.