EP0061407B1 - Method to adjust the composition of a zinc alloy for tempered galvanization by adding concentrated metallic alloying additives, and compositions of the additives - Google Patents

Description

The invention relates to a process for adjusting the composition of a zinc alloy, intended for the dip galvanizing of steels, including silicon steels, the alloy consisting of zinc of commercial purity with a weighted content. from 1000 to 15000 ppm of lead and as additives of aluminum, tin and magnesium at weight contents selected in the respective ranges (AI) 100 to 5000 ppm, (Sn) 300 to 20 000 ppm, and (Mg) 10 to 1000 ppm, the process consisting in adding, to the molten zinc alloy, deficient in at least one additive, at least one metallic composition, soluble in molten zinc, and comprising with a relatively high content at least one additive in quantity such that the deficit is compensated for. The invention also relates to metallic compositions suitable for implementing the method.

French Patent 2,366,376, filed on October 1, 1976 under No. 76 29545 and issued on October 27, 1980, describes an alloy corresponding to the aforementioned composition, and which proves effective in the dip-galvanizing of steels with silicon, usually designated by semi-quenched, quenched, and high silicon steels.

We will briefly recall the effect of the components of this alloy. Zinc with commercial purity corresponding to AFNOR NFA standards, classes Z6 and Z7 has maximum contents defined in Copper, Cadmium and Iron. In addition, it has maximum lead contents (15,000 p.p.m. for class Z6, 5,000 p.p.m. for class Z7). These lead contents, originally defined by the conditions for the production of zinc, have proved to be favorable for galvanization by lowering the viscosity of the molten zinc, so that they have been maintained while the evolution of the processes metallurgical allows the production of zinc with lead contents lower than 1000 ppm Frequently the categories Z6 and Z7 are currently obtained by adding lead to zinc.

The presence of aluminum reduces the reactivity of the iron / zinc couple, and at the levels indicated above, the reactivity of zinc vis-à-vis silicon steels. Tin and magnesium are active in reducing or eliminating the lack of coverage caused by the alumina formed by oxidation of aluminum. The simultaneous presence of tin and magnesium leads to remarkable results.

However, dip galvanizing baths see their composition evolve during operations, the oxidation rates of components, zinc, lead and additives, at the operating temperature (around 450 ° C) and in the presence of galvanizing flux (zinc and ammonium chlorides) being different, and practically all the higher as the metal is oxidizable. Oxidation occurs on the surface of the bath, and in contact with the flow and the air entrained by the parts during their immersion. The additive deficits as a result of oxidation relate mainly to magnesium and aluminum.

Now precisely the additions of aluminum and magnesium present particular difficulties, linked to the low density of these metals, to their high oxidability, and to a certain extent to the fact that these metals are not liquid at the temperature of zinc baths. molten around 450 ° C. In fact, during the phase which precedes the complete dispersion of the additions by diffusion, these light metals float on the surface of the bath where they are exposed to oxidation by ambient air. The diffusion rate is a function of the diffusivity of the additive metals in zinc at 450 ° C, and of the effective contact surface between phases. Although the diffusivities of aluminum and magnesium are relatively high, the contact surface is reduced on the surface of the immersed parts of the blocks of additive metals, and the diffusion efficiency is greatly reduced by the presence of a layer of 'oxides at the interface. The oxidation of aluminum and magnesium metals, under these conditions, is preponderant over dispersion. There is no point in fragmenting the additive metals to increase the contact surface with molten zinc, the surface offered for oxidation increasing in the same proportion. Finally, at 450 ° C, magnesium, especially finely fragmented, may ignite and cause explosions. In contrast, tin, with density and melting points close to those of zinc, and having a diffusion speed comparable to that of these metals, is easily added to zinc. Lead, which diffuses badly would tend to collect at the bottom of the bath, is the least oxidizable of the elements present, and hardly ever requires addition in the galvanizing bath.

It is known in metallurgy, to provide a base metal with alloying elements in metered quantity, to add metallic compositions where the alloying elements are relatively concentrated to the molten base metal. However, if this concept is known per se, the natures and contents of the constituents of the metallic compositions must be determined as a function of the properties required, and, if several compositions must be used simultaneously, of their compatibility.

It will be noted that, from the moment when we are able to make up for the deficit of each of the additives of the galvanizing alloy, we will thereby be able to constitute this alloy from zinc of commercial purity and we will complete the alloy by adding, to the molten zinc, missing additives. In other words, adjusting the composition of the alloy means developing this alloy as well as restoring its previous composition to it.

The invention therefore proposes a method for adjusting the composition of a zinc alloy, intended for the dip galvanizing of steels, including silicon steels, the alloy consisting of zinc of commercial purity with a weight content of 1 000 to 15000 ppm lead, and as additives, aluminum, tin and magnesium at weight contents selected from the respective ranges (AI) 100 to 5,000 ppm, (Sn) 300 to 20,000 ppm and (Mg) 10 to 1,000 ppm, process according to which we add. to the molten zinc alloy, deficient in at least one additive, at least one metallic composition soluble in the molten zinc and comprising at relatively high content at least one additive, in an amount such that the deficit is compensated for. characterized in that, while the tin composition is this metal in the practically pure state, the magnesium composition is a ternary zinc, magnesium, aluminum alloy with by weight 5000 to 50,000 p: pm of magnesium and 10 to 500 ppm of aluminum, and the aluminum composition, n added in quantity which takes account of the possible addition of ternary zinc / magnesium / aluminum, is a binary zinc / aluminum alloy, with an aluminum content by weight close to 5%.

It has already been reported that the addition of tin to molten zinc was not a problem. We chose, to provide aluminum without practically modifying the content of the other additives, a zinc aluminum eutectic, having a melting point of 385 ° C. This alloy known per se is at 450 ° C significantly less oxidizable than aluminum, due to the dilution of this metal in zinc. The choice of metallic composition for the supply of magnesium presented some difficulties. The binary zinc magnesium eutectic, at 30,000 p.p.m. of magnesium, has a solidification point at 367 ° C; but the binary zinc / magnesium alloys close to the eutectic are too fragile to be shaped into manipulable ingots. The addition of aluminum makes it possible to remedy the fragility. The ironing action of aluminum, for magnesium contents, close to that of eutectics, begins to be sensitive from 10 p.p.m.

Of course, the composition chosen from the zinc alloy for galvanization will correspond to the preferred compositions presented by French patent 2,366,376.

However, the continuation of the work which has led to the above-mentioned galvanizing alloy compositions has revealed the advantage of adding zinc of commercial purity to 1000-15000 ppm of lead and aluminum, tin and magnesium additives, beryllium to weight contents of between 4 and 100 ppm by reducing the surface oxidation of the molten alloy, and the flow of the molten alloy on the surface of the parts after leaving the bath. Beryllium is very poorly soluble in pure zinc (around 450 ° C. the solubility is of the order of 100 p.p.m.) and it is practically excluded to provide beryllium in the form of zinc / beryllium binary. The solubility of beryllium in common metals is only notable for copper, nickel, iron and aluminum. Nickel and copper are metals to be avoided in the considered galvanizing coatings. Iron could have been tolerated in view of the traces of iron which inevitably dissolve in the alloy during the immersion of steel parts. But beryllium iron alloys hardly dissolve in zinc at 600 ° C. The beryllium supply is obtained using a ternary zinc / aluminum / beryllium alloy, produced by dissolving an aluminum beryllium alloy containing 4-8% beryllium in pure zinc. The weight composition of the ternary alloy is: aluminum 5,000 to 50,000 p.p.m., beryllium aluminum weight ratio 11.5 to 24 and zinc the rest.

It should be noted that the term zinc is used here in its usual meaning as a base metal containing common impurities at levels where the properties of the metal, in relation to the intended application, are not appreciably affected. A distinction is thus made between impurities from alloying elements or additives which, at the specified contents, act on the properties of the base metal, in relation to the intended application. However, when the base metal contains, as initial impurity an element which is intended as an additive, at a content significantly higher than that of the initial impurity, the content as an additive is understood to be the sum of the initial content in impurity, and the amount of additive added thereafter.

A preferred composition by weight of galvanizing alloy with aluminum, tin, magnesium and beryllium additives corresponds to: tin 500 ± 25 ppm, aluminum 375 = 25 ppm, magnesium 60 ± 3 ppm and beryllium 6.5 ± 0.5 ppm, zinc at 1000-15000 ppm of lead constituting the remainder.

The preferred ternary alloys for supplying magnesium and beryllium respectively have weight compositions of magnesium 30,000 ± 1,500 ppm, aluminum 100 ± 5 ppm, and aluminum 9,000 ± 450 ppm, beryllium 470 ± 50 ppm, in both cases the rest being zinc.

To avoid having to control the content of a dip galvanizing bath too frequently, it is possible to systematically compensate for the losses of additives which are consumed during the galvanization, by additions of metallic compositions. Tests have shown that per tonne of galvanized steel articles, 2 to 25 kg of beryllium ternary and 0.5 to 5 kg of magnesium ternary should be added; preferable addition values are 12.5 ± 0.6 kg of beryllium ternary and 1.4 ± 0.07 kg of magnesium ternary.

The characteristics and advantages of the invention will become apparent from the description which follows, illustrated by examples.

The developments relating to the alloy for galvanization which is the subject of French patent 2,366,376 have shown, as it was qualitatively foreseeable, that, during dip galvanizing operations, the composition of the zinc alloy in fusion changed, with a depletion of the most oxidizable additives as parts are galvanized. This slow oxidation on a quiescent bath on which a layer of protective oxides is formed, is greatly accelerated by the action of galvanizing fluxes (zinc and ammonium chlorides), and the air entrained by the parts. immersion. The reaction products of the flux and of the alloy, in the presence of air (chlorides, oxides, oxychlorides ...), are partly volatile, and for another part form the superficial dross eliminated by scraping or spatulation. It was therefore very advantageous for users of the galvanizing alloy to be able to periodically readjust the composition of the molten alloy to its original composition, in order to avoid having to empty the tanks where the alloy had reached the suitable composition limits, and reconstitute the baths with new alloy. These operations for renewing the dip galvanizing baths were found to be costly, at least in terms of installation and handling downtime, if the alloy manufacturer took back the used alloy to renovate it.

Among the constituents of the alloy, zinc, which constitutes at least 95% of the alloy by weight, can withstand some losses by oxidation without the composition of the alloy being substantially modified; lead and tin, less oxidizable than zinc, suffer only negligible losses by oxidation. On the other hand, aluminum and magnesium disappear by oxidation relatively quickly. The readjustment of the composition of the alloy requires preferential additions of aluminum and magnesium.

However, if additions of tin (density 7.34 melting point 231.8 ° C) and zinc of commercial purity (density 7.14 melting point 419 ° C) present no difficulty in adding to a bath zinc alloyed at a temperature of about 450 ° C, it is not the same for aluminum (density 2.7 melting point 658 ° C) and magnesium (density 1.74 melting point 651 ° C) . The dissolution of these latter metals can only occur by diffusion in molten zinc; due to their low density they tend to float on the zinc bath. In addition, the alumina layer on the surface of the aluminum forms a screen for the diffusion of the aluminum. Finally, at the temperature of the zinc bath, the magnesium oxidizes in depth, and is close to its spontaneous ignition temperature in the air. Moreover, for the normal development of the galvanizing alloy, one operates so as to minimize the oxidation of aluminum and magnesium by preventing them from being in contact with air.

• - ne contenir que des métaux entrant dans la composition de l'alliage de galvanisation ;
• - ne pas être trop rapidement oxydables à la température de fusion, et ne pas nécessiter de précautions anormales d'emploi ;
• - de préférence posséder un point de fusion voisin de 450 °C, pour aider la diffusion par une dispersion de l'additif fondu.

It was therefore necessary to add aluminum and magnesium in the form of metallic compositions or alloys which meet the following criteria:

• - contain only metals used in the composition of the galvanizing alloy;
• - not to be too rapidly oxidizable at the melting temperature, and not to require abnormal precautions for use;
• - Preferably have a melting point close to 450 ° C, to help the diffusion by a dispersion of the molten additive.

In addition, to allow flexibility in adjusting the composition of the galvanizing alloy, it is desirable that each of the metal compositions used be assigned to a particular additive metal, in the sense that the concentration of the additive targeted in the composition must be much higher than the concentration in the alloy, while the concentration ratios of the other metals in the composition are not too far from what they are in the alloy or at least that the concentration ratios of the constituents of the composition compared to that of the targeted additive are significantly lower than the ratios in the alloy.

With regard to aluminum, there is a zinc aluminum alloy 5% by weight of aluminum, its composition corresponding to the eutectic at melting point 385 ° C., and is therefore suitable as a metallic composition assigned to aluminum. .

Regarding magnesium, there is a zinc / magnesium eutectic at 3% by weight of magnesium, with a melting point of 367 ° C. , or during transport and essential handling. The compositions sufficiently close to the eutectic to have an acceptable melting point (less than about 450 ° C.) are practically also too fragile. But it turned out that the addition of small amounts of aluminum significantly reduced the brittleness of the zinc / magnesium binaries. The effect begins to be felt at 10 p.p.m. (by weight) of aluminum. In addition, the presence of aluminum reduces the oxidation of magnesium when the ingot is poured. Around 100 p.p.m. of aluminum, the brittleness practically no longer decreases when the aluminum content increases; it is unnecessary to exceed 500 p.p.m. of aluminum, no advantage compensating for the loss of flexibility in adjusting the composition of the galvanizing alloy; this loss of flexibility resulting from the fact that a deficit in magnesium alone is compensated for by an enrichment in aluminum. Obtainable metal compositions are obtained with 5000 to 50,000 p.p.m. by weight of magnesium and the quantities of aluminum mentioned above. We prefer a composition close to eutectic with 30,000 ± 1,500 p.p.m. of magnesium and 100 ± 5 p.p.m. of aluminum.

Example 1 Elaboration of a ternary zinc, magnesium, aluminum.

In an industrial frequency induction furnace, with a 150 liter crucible, equipped to work in a controlled atmosphere, 485 kg of Z9 quality zinc is melted under a neutral atmosphere; the temperature of the liquid zinc is brought to 600 ° C. and 15 kg of magnesium at 99.9% purity are added; then 50 g of aluminum at 99.5% purity are added. The temperature is then lowered to around 500 ° C and maintained at this temperature for 15 minutes, so that the electromagnetic stirring ensures the homogeneity of the alloy. Then the heating is switched off, and the alloy is poured into cooled ingot molds when the temperature is between 450 ° and 420 ° C.

Example 2 Constitution of a tin, aluminum, magnesium galvanizing bath.

In a galvanizing tank with a capacity of 150 tonnes of zinc, 80 tonnes of zinc Z6 at 1.4% lead are put, 67.3 tonnes of zinc Z7 at 0.45% lead, 375 kg of tin, and 1 , 8 tonnes of zinc aluminum alloy at 5% by weight of aluminum. After melting the metals, 500 kg of alloy produced according to Example 1 are added. An analysis of the bath gives by weight Lead 9,500 ppm, Tin 2,500 ppm, Aluminum 60C ppm, Magnesium 99 ppm, the remainder being Zinc with the usual impurities with a tolerated content.

• - une réduction de la vitesse de formation d'une couche superficielle d'oxyde sur les bains en fusion ;
• - un meilleur écoulement du zinc fondu sur la surface de pièces à la sortie du bain de galvanisation, cet effet résultant sembie-t-il de la réduction de l'épaisseur et de la ténacité de la couche d'oxyde sur le recouvrement de zinc, cette couche d'oxyde retenant l'excès de zinc ;
• - une amélioration de la facilité d'évacuation des crasses superficielles vers les bords de cuve en préalable à l'émersion des pièces, opération dite couramment spatulage.

Additional work on alloys for galvanization by immersion has shown that beryllium, known as an element reducing the oxidation rate of foundry alloys based on aluminum or zinc, has fabulous effects on alloys for galvanization:

• a reduction in the rate of formation of a surface layer of oxide on the molten baths;
• - a better flow of the molten zinc on the surface of parts at the exit of the galvanizing bath, does this effect seem to result from the reduction in the thickness and the tenacity of the oxide layer on the zinc coating , this oxide layer retaining excess zinc;
• - An improvement in the ease of evacuation of superficial dirt towards the edges of the tank prior to the emersion of the parts, an operation commonly known as spatulation.

The action of beryllium is felt for very low contents, from 4 p.p.m. (by weight). Beyond 100 p.p.m. it is observed that there occurs, at the usual temperature of the galvanizing baths in operation, a segregation of beryllium which collects on the surface and is evacuated with the dross. It has also been found, from 15 ppm by weight of beryllium, for baths with a relatively high aluminum content, greater than 550 ppm, a synergistic action of aluminum and beryllium on the kinetics of the iron-zinc reaction (formation of intermetallic compounds).

During the preparatory work, studies on the solubility of beryllium in zinc were consulted, starting from sintered alloys of beryllium with 99% purity and pure zinc. The liquidus curve on the binary diagram goes through the following points:

This table shows that, even using a binary alloy of composition corresponding to the liquidus at 696 ° C, and cooled sufficiently quickly so that the beryllium remains in supersaturation, the tonnages to be used so that the final alloy is in the range 4- 100 ppm represent from 0.5 to 12.5% of the total mass of the alloy, that is to say for a 150-ton bath, from 0.75 to 18.75 tons. Furthermore, the diffusion of beryllium in molten zinc, at temperatures far from the melting point of beryllium (1 2800C) is slow, and the development of the binary alloy at temperatures above 700 ° C is difficult due in particular to the vapor pressure of zinc (boiling point 910 ° C). The development of such alloys is prohibitive on an industrial scale.

To introduce relatively high contents of beryllium in zinc, it has been imagined to bring this beryllium in the form of an alloy readily soluble in molten zinc at reasonably high temperatures, this alloy preferably being a commercially available alloy, for obvious reasons of cost price. Common alloys Cu-Be at 4%, AI-Be at 5%, Fe-Be at 10% and Ni-Be at 25% have been found. The presence of copper or nickel in dip galvanizing baths is practically excluded or at least strictly limited. as iron is always present in the galvanizing baths of steel parts due to the dissolution of iron from steel parts as a result of the dissolution of the iron of the pieces, we could have tolerated adding a little iron. The beryllium iron binary was found to be practically insoluble in zinc at 600 ° C; after 48 hours at this temperature, the quantities of dissolved iron-beryllium alloy are imponderable.

On the other hand, good results have been obtained by dissolving 5% aluminum beryllium alloy in zinc, at a temperature where this alloy is molten. In practice, a binary alloy containing 4 to 8% beryllium by weight can be used, so that the weight ratio aluminum / beryllium in the ternary alloy will be between 24 and 11.5. The aluminum contents of the ternary must be such that the melting point is of the order of 450 ° C., ie 0.5-5% by weight. However, it is preferable to use an aluminum content at the bottom of the indicated range to reduce the tendency for beryllium to segregate.

Example 3 Elaboration of a zinc-aluminum-beryllium ternary.

In the induction furnace used in Example 1, 495 kg of zinc Z9 is melted under a neutral atmosphere. The temperature is raised to around 600 ° C. and 4.75 kg of beryllium aluminum alloy containing 5.25% beryllium are added. The temperature is maintained at 600 ° C. until intimate dispersion of the beryllium aluminum in the zinc, under the action of electromagnetic stirring. Then, as soon as the power is turned off, the alloy is poured into energy-cooled ingot molds.

The addition of beryllium has also made it possible to somewhat reduce the tin bath contents, since tin is intended in particular to take over from magnesium when the content of the latter metal has lowered in the bath by oxidation, and that beryllium reduces the rate of magnesium oxidation.

Example 4 Creation of a tin, aluminum, magnesium, beryllium galvanizing bath.

In a 150-ton capacity galvanizing tank, 147 tonnes of zinc Z7, 0.31% by weight of lead, 75 kg of tin and 750 kg of binary zinc aluminum to 5% aluminum are put. It is brought to melting temperature. Then, when the whole bath is in fusion, 300 kg of zincmagnesium-aluminum ternary prepared according to Example 1 are added, and 2020 kg of zinc-aluminum-beryllium ternary prepared according to Example 3.

An analysis of the bath gives by weight: lead 3,000 p.p.m., tin 500 p.p.m., aluminum 370 p.p.m., magnesium 60 p.p.m., beryllium 7 p.p.m.

it has already been reported that the development of the use of metallic combinations concentrated in an additive had been made more specifically to allow the readjustment of the additive contents of the galvanizing alloys as the additives were used up following the galvanization of parts, the first constitution of dip galvanizing baths benefiting from the flexibility of composition allowed by the use of these metallic combinations.

The consumption of the components of the bath is due, on the one hand, to the sampling of alloy constituting the coverings of part, and on the other hand to the oxidation of some of these components in contact either with the galvanizing flux, or with the air entrained by the parts upon immersion in the molten alloy.

The work carried out by the Applicant established that, if in a strict manner the consumption of aluminum, magnesium and beryllium were appreciably proportional to the quantity of flux implemented, that is to say to the surface of the parts to be covered, it there was an equalization between thin parts and thick parts (considering a fictitious thickness ratio of volume to the surface of the part), so that the contributions in metallic compositions can be proportional to the tonnage of galvanized parts, without the composition of the galvanizing bath evolves too quickly. This makes it possible to space composition analyzes, and the corresponding readjustments of composition.

For a galvanizing alloy produced according to Example 4, it was determined that maintaining the composition required the addition of metallic compositions prepared according to Examples 1 and 3, respectively in the ranges 0.5-5.0 kg and 2, 25 kg per ton of galvanized steel.

Example 5

Maintenance of a dip galvanizing bath.

In a galvanizing tank with a capacity of 150 tonnes, containing this quantity of galvanizing alloy prepared according to Example 4, parts of structural steel are galvanized with silicon, at an average rate of 20 tonnes / day.

Tests have shown that, for parts of this kind, the composition of the bath was stabilized at best by adding 1.4 kg of ternary alloy according to Example 1, and 12.5 kg of ternary alloy according to Example 3. Consequently, the bath is added daily, preferably during a period of inactivity, 28 kg of metallic composition with magnesium according to example 1, and 250 kg of metallic composition with beryllium according to example 3.

It is possible to envisage the preparation of a quaternary metallic composition, such as that which would result from mixing the ternaries according to Examples 1 and 3, in the proportions corresponding to the maintenance additions of Example 5.

To produce such a metallic composition, 494 kg of zinc Z9 is melted under a neutral atmosphere, and the temperature is raised to 675 ° C. 1.5 kg of magnesium are added, the temperature is allowed to drop to 625 ° C., 4.25 kg of aluminum-beryllium alloy at 5.25% by weight of beryllium is added, and, as soon as the electromagnetic stirring has ensured the aluminum-beryllium dispersion, it is poured into energy-cooled ingot molds.

Of course the invention is not limited to the examples described, but embraces all the variant embodiments. In particular, the alloy compositions may vary within the range of the ranges indicated. In addition, where a composition is indicated by an encrypted content for each component, it goes without saying that the numerical value is understood as a central value in a usual range, such as ± 5%.

Claims (11)

1. A process for adjusting the composition of a zinc alloy suitable for the dip galvanisation of steels, including silicon steels, said alloy comprising zinc of commercial purity with an amount of 1,000 to 15,000 p.p.m. by weight of lead, and, as additives, aluminium, tin and magnesium in amounts selected in the respective ranges (Al) 100 to 5,000 p.p.m., (Sn) 300 to 20,000 p.p.m., and (Mg) 10 to 1,000 p.p.m., the process in which there is added to the zinc alloy in a molten state, deficient in at least one additive, at least one metal composition which is soluble in the molten zinc and which contains a relatively high amount of at least one additive, in a quantity such that the deficiency of the additive is compensated, characterized in that while the tin composition is in a practically pure state the magnesium composition is a ternary zinc, magnesium, aluminium alloy containing 5,000 to 50,000 p.p.m. by weight of magnesium and 10 to 500 p.p.m. of aluminium, and the composition of aluminium added which takes account of the optional addition of ternary zinc/magnesiumialuminium alloy, is a binary zinc/aluminium alloy having an amount of aluminium by weight in the vicinity of 5 %.

2. Process according to claim 1, characterized in that the ranges of amounts of additives of the zinc alloy are (AI) 300-600 p.p.m., (Sn) 1,000 to 3,000 p.p.m., (Mg) 20 to 200 p.p.m.

3. Process according to claim 2, characterized in that the selected amounts of additives are substantially (AI) 370 p.p.m., (Sn) 2,500 p.p.m., and (Mg) 100 p.p.m.

4. A process for adjusting the composition of a zinc alloy suitable for the dip galvanisation of steels, including silicon steels, said alloy comprising zinc of commercial purity with an amount of 1,000 to 15,000 p.p.m. by weight of lead, and, as additives, aluminium, tin and magnesium in amounts selected in the respective ranges (Al) 100 to 5,000 p.p.m., (Sn) 300 to 20,000 p.p.m., (Mg) 10 to 1,000 p.p.m., the process in which there is added to the zinc alloy in a molten state, deficient in at least one additive, at least one metal composition which is soluble in the molten zinc and which contains a relatively high amount of at least one additive, in a quantity such that the deficiency of the additive is compensated, characterized in that the zinc alloy containing as a complementary additive beryllium in an amount by weight between 7 and 100 p.p.m., the tin composition is in a practically pure state, the magnesium composition is a ternary zinc/magnesium/aluminium alloy with 5,000 to 50,000 p.p.m. by weight of magnesium and 10 to 500 p.p.m. by weight of aluminium, the beryllium composition is a ternary zinclaluminium/beryllium alloy with 5,000 to 50,000 p.p.m. by weight of aluminium, the aluminium/beryllium weight ratio being between 11.5 and 24, and the aluminium composition added in an amount which takes account of the additions of ternary zinc/magnesium/aluminium and zinclaluminium/beryllium alloys, being a binary zinc/aluminium alloy with a weight ratio of aluminium in the vicinity of 5 %.

5. Process according to claim 4, characterized in that the selected amounts of the additives are tin 500 ±25 p.p.m., aluminium 375 ± 25 p.p.m., magnesium 60 ± 3 p.p.m., beryllium 6.5 ± 0.5 p.p.m.

6. A ternary alloy with magnesium for carrying out the process according tc any one of claims 1 to 5, characterized in that it contains by weight from 5,000 to 50,000 p.p.m. of magnesium and 10 to 500 p.p.m. of aluminium, the remainder being zinc.

7. Alloy according to claim 6, characterized in that it contains by weight 30,000 ±1,500 p.p.m. of magnesium and 100 ± 5 p.p.m. of aluminium.

8. A ternary alloy with beryllium for carrying out the process according to claim 4 or claim 5, characterized in that it contains by weight from 5,000 to 50,000 p.p.m. of aluminium, and beryllium in a weight ration to the aluminium of from 1/11.5 to 1/24, the remainder zinc.

9. Alloy according to claim 8, characterized in that it contains by weight 9.000 ±450 p.p.m. of aluminium, and 470 ± 50 p.p.m. of beryllium.

10. Process according to claim 5 for maintaining the composition of the zinc alloy in the course of galvanisation of steel workpieces, by addition the ternary alloy with magnesium according to claim 7 and the ternary alloy with beryllium according to claim 9, characterized in that there is added 2 to 25 kg of the ternary alloy with beryllium and from 0.5 to 5 kg of the ternary alloy with magnesium per tonne of galvanised steel workpieces.

11. Process according to claim 10, characterized in that 12.5 ± 0.6 kg of ternary alloy with beryllium and 1.4 ±0.07 kg of ternary alloy with magnesium are added per tonne of galvanised workpieces.