NO128282B - - Google Patents

Description

Process for producing a solid, shaped product from a foamed metal consisting of aluminum alloyed with at least 1.2% by weight of magnesium, silicon or tin.

The present invention relates to a method for

production of foamed aluminum meta11.

Foamed metals have previously been described, see e.g.

U.S. Patents 2,895,819, 3,300,296 and 3,297,431. Typically, such foams are made by adding a gas-evolving compound to a molten metal and heating the mixture to decompose the compound to form an off gas. The gas expands and causes the metal to foam up. After the foaming, the resulting product is cooled to form a foamed solid. The gas-foaming solid may be a metal hydride, such as TiH2. ZrH 2 or lithium hydride, see US Patent 2,983,597. Many prior art foams exhibit cells of non-uniform structure or an undesirably large size. A main reason for this is the inability to develop ese gas and disperse it through the mass to be foamed at optimally desired speeds. There is thus a need for a method to increase the viscosity of the molten metal in order to be able to support the etching step. The present invention satisfies this need.

According to the invention, a method is provided for the production of a solid, shaped product, from a foamed metal consisting of aluminum which is alloyed with at least 1.2% by weight, preferably 2-35% by weight, of magnesium, silicon or tin, where a thickening agent is mixed with the molten alloy and then a blowing agent, such as a hydride of zirconium, hafnium or titanium is added, after which the alloy is allowed to solidify. The method is characterized by the fact that a thickening agent is used which is normally gaseous under the working conditions and consists of oxygen, carbon dioxide, nitrogen, air, water or an inert gas such as argon.

US patent 3,300,296 describes a silicic acid-containing non-metallic aggregate in the melt as a thickening agent. This entails the obvious disadvantage that a solid foreign substance is thereby introduced which will remain in the product. It has also been shown that the product obtained in accordance with the state of the art is far less satisfactory than the product produced according to the present invention. This is evident from the data given below which indicate the properties of six foaming aluminum alloy samples. Sample A was prepared in accordance with the present method, the so-called Ethyl process and sample C was prepared according to the method according to US patent 3,300,296

DATA ON FOAMED ALUMINUM/MAGNESIUM ALLOY SPECIMENS

NOTES REGARDING THE SAMPLES AND THE MANUFACTURE

A. The alloy used was an aluminium-magnesium-

alloy that contained 7% by weight of magnesium and approx. 92.3% aluminium. The alloy was melted and oxygen was introduced with stirring which

a thickening agent prior to the addition of zirconium hydride as a blowing agent. The material was poured or cast and solidified into large blocks or slabs or so-called "biscuits" and sawn into slabs of 2.5 cm thickness. The density of the sample was 0.229 kg/liter (14.3 Ibs. per cu.ft.) which corresponds to a relative density compared to the solid alloy of 0.0875.

B. This sample is believed to represent the best mate-

riale which is produced according to the previously known method as represented by US patent 2,983,597. An alloy corresponding in general to the above-mentioned alloy A was used, namely with approx. 1% magnesium metal. The manufacturing process was as stated in the patent, zirconium hydride was added under vigorous stirring to the molten aluminum alloy. Foaming resulted and the molten foamed mass was cooled and solidified. An average density of 0.189 kg/liter (11.8 lbs/cu.ft.) was obtained.

This corresponds to a relative density, similar to the meltable alloy, of 0.072. The sizes of the voids in the solidified product were highly variable.

C. The procedure in this case was based on that technique

which is disclosed in US Patent 3,300,296. The alloy used contained approx. 2.5% by weight magnesium and approx. 0.4 wt% chromium. 890 parts by weight were melted and 26.7 parts of 115 mesh vermiculite was added at 660°C. It was not possible to add at 610°C,

because the metal was not sufficiently liquid at this temperature. The addition required 1.5 minutes and resulted in some foaming.

After stirring, an additional 8.9 parts of 10 mesh vermiculite, containing 0.44 parts of H2O, was stirred in for approx. 20 seconds at 660°C.

Chargens foamed up and solidified. The solidified material

showed a medium density of approx. 0.94 kg/litre (59 Ibs per

cu.ft.). This is a relative density of approx. 0.35, based on the density of the solidified alloy.

D. In this process, the procedure was followed according to . example 3 in US patent 3,300,296. The alloy (ACOA4043) contains

held approx. 5% silicon, and 95% aluminum with a density of approx.

2.679 kg/liter (167 Ibs. per cu.ft.). To 988 parts of the molten alloy was added 39.4 parts of 115 mesh vermiculite with stirring over a period of 1 minute at 660°C. To this was added 98.5 parts of a powdered mixture of zirconium hydride and a eutectic alloy of 33% magnesium and 63% aluminium.

It was stirred for 1.5 minutes at 660°C. The charge foamed and it

was cooled and solidified. The resulting solid foam product had an average density of 0.54 kg/liter (34 Ibs. per cu.ft.), which is approx. 0.203 in relation to the solid homogeneous alloy.

E. This sample was manufactured in accordance with US patent

3,300,296 example 4. An alloy similar to that used in sample A was used. To 865 parts were added, during re-

stirring, 60.5 parts of 15-50 mesh vermiculite for a period of approx.

4 minutes. The temperature was increased to 680°C and the charge foamed and it was cooled and solidified. The density range of the solidified sample was from 0.449 to 0.60 kg/liter (28 to 38 lbs/cu.ft.),

the samples showed a density of 0.60 kg/liter (38 lbs/cu.ft.) or a relative density of 0.207 compared to the solid alloy.

F. The procedure for this test was based on example 1 in US patent 3,300,296, followed by the addition of zirconium

hydride. To 745 parts of" a molten alloy *of the same composition as for samples A and E was added 22.2 parts of 115 mesh vermiculite at 670°C. Then 4.5 parts of zirconium hydride were added at 680°C and it found place a vigorous foaming. After solidification, densities of from (17 to 22 lbs/cu.ft.) ;0.272 to 0.352 kg/liter could be observed. Samples F had a density of 0.28 ;kg/liter (17.5 lbs /cu.ft.), or a density relative to the solidified alloy of 0.107. ;The viscous melts produce better foam than alloys not treated with viscosity-increasing or thickening agents. The metal foam products are useful as construction materials, e.g. as outer wall fields. The non-stoichiometric blowing agents are advantageous, as they release hydrogen more slowly. ;Typically, molten aluminum and molten aluminum alloys have a viscosity of the same order of magnitude as the viscosity of water. When such alloys are treated with a viscosity-increasing agent according to the invention , it can be stated is added to a much "thicker" melt. In general, the thickness is proportional to the amount of added agent. It is actually possible to produce a material that is so thick that it cannot be stirred using powerful stirring devices. The term viscosity is used here to denote the fluidity of a liquid. (In a technical sense, fluidity is the reciprocal of viscosity or apparent viscosity.) A liquid will flow slowly - have less fluidity - as viscosity increases. There are two types of viscosity, true viscosity and apparent viscosity. Apparent viscosity refers to the viscosity corresponding to the appearance and mobility of a liquid which, when measured with a viscometer, produces no or only a slight change in the true or real viscosity. An example of a material that exhibits apparent viscosity is whipped cream. It is not known with certainty to what extent the viscosity-increasing treatment according to the invention results in an increase of the real and/or apparent viscosity. Nevertheless, the viscosity increasing agent changes the aluminum alloys. from ...a material with roughly the same resistance to flow as water, to substances that are much less fluid. It turns out that the increase in viscosity is a major increase in apparent viscosity and a minor increase in real or true viscosity. We have found that viscosity-increasing treatment of an aluminum alloy with 1% magnesium increased the viscosity (according to viscosity measurement) only by approx. 16 cP. When such a molten alloy is treated, e.g. with the method indicated in the following examples, the alloy nevertheless becomes so thick that it will not be possible to pour it out of a spoon even when the spoon is turned around. Thickened aluminum alloys according to the invention give metal foam - which is better than foam from alloys which have not been treated in accordance with the invention. In foam produced according to the invention, the pore size is smaller and more uniform. The use of a viscosity-increasing agent according to the invention also makes it possible to use a smaller amount of the emulsifier than would otherwise be necessary*

C02 treatment is e.g. an advantageous preliminary step before etching with a metal hydride; Application of a C02 treatment according to the invention makes it possible to use less hydride, such as TiH2 or ZrH2. After the treatment with CO, according to the invention, one needs, among other things, not to use so much Til^ / e.g., to achieve the desired degree of foaming. The reduction of the amount of TiH2~ or ZrH2 that is required is in no way related to the degree of expansion -with C02• We have e.g. found that C02 pre-treatment will result in 0.6 g ZrH2 giving the same expansion as 1.0 g gives in the absence of C02 pre-treatment. This leads to significant savings with respect to production costs.

You can calculate how much hydrogen gas is required to achieve a desired degree of foaming. The amount of hydrogen gas is appropriately expressed as theoretical amounts. A theoretical amount is the amount of gas that will be developed (if the gasifying solid is completely decomposed) to give a known void volume in a mass - which can be expressed in the weight of the foam product per volume unit, e.g. g/ml. To obtain a foam product with a weight of 0.24 kg per liter, 2.5-3.0 theoretical amounts of TiH2 are required and this corresponds to 0.8-1.0 g TiH2 per 1000 g of metal. However, after C02~ treatment is required to

get a corresponding foam product only 1.2-1.7 theoretical amounts or 0.4-0.6 g TiH2-

Zirconium hydride, hafnium hydride and titanium hydride have the formulas ZrH2, HfH2 and TiH2, respectively. The commercial products usually contain somewhat less hydrogen than the stoichiometric amount. Commercial hydrides can thus exhibit 1.98 mol of hydrogen per moles of metal. We have found that better results are achieved if the hydrides are heat treated or annealed before use. Heat treatment (the hydride is exposed to temperatures from approx. 100 to approx. 400°C for a time

of from 1 to 24 hours) gradually removes hydrogen. When the composition becomes from 1.65 to 1.80 moles of hydrogen per mole of metal, an excellent foaming agent is obtained. These agents provide hydrogen at a reduced rate. There will therefore be more time to mix the materials with it

molten metal. This increased time will therefore give a more even mixture. Such admixture and the slower release of hydrogen result in smaller and more uniform pore sizes.

Viscosity-increasing agents used according to the invention are argon, nitrogen, air, oxygen, carbon dioxide and water. The mechanism by which these agents increase the viscosity of molten alloys is not known, and furthermore the mechanism may be different in each individual case. It is believed that argon increases the viscosity by some physical mechanism. On the other hand, chemical aspects can come into play when thickening down C02" Experimental indications of this are that in some cases small surface fires occur when the molten alloy is treated with C02- In some cases an acetylene-like smell has been observed with C02- treatment.

The physical state of the viscosity increasing agent is not of critical importance. One can e.g. use solids, liquids or gases. E.g. C02 can be present in gaseous or solid state, water can be used as liquid water, ice or steam. Nitrogen can be used as a gas or as a low-temperature liquid. The thickener can be used in any physical state that it can exhibit, and an increase in viscosity can be achieved.

To achieve the thickening, the viscosity-increasing agent is added to the molten alloy. Solidification is avoided by working at sufficiently high temperatures. The temperatures used are usually within the range of from 20 to 90°C above the melting point of the alloy. We have noted that the increase in viscosity is of shorter duration at higher temperatures.

In general, the temperatures used are above 600°C, but lower than 760°C. For many alloys, the recommended temperature range is from approx. 650 to 720°C. At these temperatures, the increase in viscosity is fairly permanent. In many cases, the increase will last approx. half an hour' or more. This is a sufficient time for the further processing for the production of foam. The viscosity increase will remain even after short exposures to somewhat higher temperatures. If it is desired to maintain the viscosity for longer periods, more of the thickener can be added when the molten alloy begins to "thinner".

The duration of the viscosity increase appears to be inversely proportional to temperature. If, however, you wish to work at higher temperatures, you can add more of the viscosity-increasing agent. The increased amount of the agent can be added from the start or, if desired, it can be added in partial amounts as the mixture begins to thin.

To achieve the viscosity increase, the viscosity increase must

the agent is mixed into the molten alloy. It is m.a.o. not enough just to treat the surface of. the forge with the agent. The agent must thus be mixed into the molten mass to be treated. The-

tea can be made by any mixing technique, such as e.g.

an efficient stirring.

The amount of viscosity-increasing agent that must be added is not known with absolute certainty. This is because there is no way to avoid the loss of any agent when the mixture is carried out. The loss has some resemblance to the removal of water droplets placed on a hot pan. This loss is due to the difference between the temperature of the molten alloy and the viscosity increasing agent. As will be seen from the use of liquid air or nitrogen, or solid C02 /

the temperature difference can be very large.

Using a stirring rate of 100 to

3000 rpm usually from 0.25-6.0 g of the viscosity-increasing agent is used per 100 g of the alloy, preferably from 0.5-5.0 g.

More advantageously used for:

C02 from 1-3 g

H20 1 to 6 g

air 0.5 to 3' g

N2 1 to 4 g

argon 1 to 4 g

per every 100 g of the alloy.

The viscosity increasing agent should be added rapidly, preferably over a period of 15 seconds to 3 minutes. The time can be increased if a relatively large amount of the agent is used.

The pressure at which the viscosity increasing agent is added to the molten alloy is not critical. Thus, sub-atmospheric pressure, super-atmospheric pressure or pressure from the surrounding atmosphere can be used. In most cases, no particular advantage is gained by applying pressure less than the ambient pressure. Ambient pressure is preferred. However, in some cases it may be advantageous to use increased pressure, e.g. up to 105 kg/cm 2. Such pressures mean that the foaming agent is forced to mix with the molten alloy, the closed vessel and the increased pressure inhibit the escape of the viscosity-increasing agent.

The viscosity-increasing agents according to the invention do not act in all respects as an ese gas such as hydrogen. They give much less expansion than an equivalent amount of hydrogen. E.g. the expansion due to CO, is in some cases only 1/8 to 1/10 of the expansion caused by an equivalent amount of hydrogen. In some cases, the expansion due to CO2 is less.

The increase in viscosity from the agents according to the invention is due to the presence of a promoter metal alloyed with aluminium. Suitable promoter metals are tin, silicon and magnesium. Such metals should be present in at least an amount to provide 1.2% by weight of promoter metal. We do not know of any critical upper limit for the amount of promoter metal, but it is preferred to use aluminum alloys containing from 2 to 35% by weight of promoter metal. Alloys with up to 7 wt% promoter metal are preferred. Alloys with from 4 to 7% by weight of magnesium are particularly advantageous. In many cases, the following general rules can be stated as applicable:

(1) for a given amount of viscosity increasing agent, the increase in viscosity is proportional to the amount of promoter metal. (2) The increase in viscosity is proportional to the amount of viscosity-increasing agent used. (3) The higher the temperature, the shorter the duration of the viscosity increase. (4) The higher the temperature, the more agent is required to

give a specific viscosity increase.

A large number of different foaming agents can be used in the foaming process according to the invention. In general, all previously known spray agents can be used. Certain antiperspirants are actually better than others. For any blowing agent, nevertheless, the foam products obtained according to the invention have significantly smaller and uniform pore sizes than foam products made from the same metal substrate, but which have not been made more viscous.

Of all the known blowing agents, it is preferred to use metal hydrides. Of these, it is preferred to use complex or simple hydrides which have the best acid properties. Such hydrides are those which decompose to give gaseous hydrogen at the temperature of the material to be foamed and which release the gaseous hydrogen at a not too high rate. Of such hydrides, preference is given to titanium, hafnium or zirconium hydrides, especially the latter. It is possible to use "dihydrides" of the type available in the trade as well as heat-treated hydrides with a composition less than the stoichiometric.

The amount of hydride (or another foaming agent) used depends on the desired degree of foaming. If it e.g. if it is desired to produce a dense foam product, then less of the foaming agent is used than when a lighter foam product is to be produced. It is preferred to produce foam products with a 20% specific gravity or less. Expressed in another way, it is preferred to produce foam products that do not weigh more than approx. 20% by weight - of the non-expanded metal.

For such foam products, from 0.2 to 1.0 g of commercial HfH2, TlH2 or ZrH2 are used per every 100 g of molten metal to be foamed. A preferred range is from 0.5 to 0.6 g.

A lower temperature limit must be exceeded to produce foam.

This lower limit is easily understood. A temperature is used above which the metal to be expanded is molten and above the temperature required to provide the gas required to effect the foaming. In this regard, it is also desirable to use a foaming temperature at which the tail gas is not formed at an uncontrollable rate. Furthermore, a temperature is used at which the melt is sufficiently viscous. Taking these considerations into account, foaming is carried out at temperatures "within the range from 650 to 800°C and it is preferred to use temperatures from 670

to 705°C.

It is preferred to carry out the foaming process at ambient pressure. Greater or lesser pressure can be used. In many cases, no particularly beneficial effect is achieved by the use of sub-atmospheric pressures, and such pressures can be harmful as they can encourage the development of tail gas outside the bounding walls of the mass to be foamed. When it is desired to use super-atmospheric pressures, pressures up to e.g. 105 kg/cm<2> or higher.

As indicated above, foaming is carried out using molten metal masses that have been made more viscous. It is used i.a.o. masses that have been previously treated with a viscosity-increasing agent. It is naturally not desirable to use pulp that has lost the required increased viscosity. Consequently, it is preferred to use pre-treating masses which have been made more viscous within approx. half an hour after the viscosity-increasing work step. Naturally, molten alloys that have been made more viscous more than half an hour before the etch step can be used if the required viscosity is still present. In this connection, it may be worth mentioning that the increase in viscosity will last longer if the alloy has been made more viscous in the first stage or if more viscosity-increasing agent is added when the alloy begins to thin. The addition or introduction of the viscosity increasing agent can be carried out once, twice or more often as required.

When the foaming step is carried out according to the invention, the foaming agent must be mixed with the molten mass to be foamed. The more even the mixture is, the better the foam product will be. Any mixing method known to effectively mix materials in a liquid state can be used. It is preferred to use efficient stirring and it is preferred that the blowing agent-alloy mixture is substantially homogeneous in as short a time as possible. In most cases, good results are obtained when the blowing agent-alloy mixture is substantially homogeneous within 1 minute or less, but it is preferable to use such agitation as will provide substantially homogeneity within 10 seconds.

For °. to facilitate the understanding of the production of a metal foam according to the method, the following preferred exemplary method shall be stated:

(1) Approx. 4000 g of the alloy is heated in an induction vessel to 700-760°C. (2) After melting, the melt is stirred so that essentially the entire amount of it is moved with a high viscosity at approx. 100-3000rpm. (3) 10-60 g of powdered C02 is added per 1000 g of alloy over a period of 1-3 minutes.

Some flare-up and an acetylene-like odor may occur. (4) The viscous mixture is brought to the temperature desired for the foaming step, 650-800°C (a preferred range is from 670-705°C). (5) Sufficient foaming agent is added to give the desired foam density. When zirconium hydride is used, sufficient hydride is added - for mixing into the mass to be converted - approx. 1.2 g ZrH2 per 100 g of the alloy for a foam product weighing 0.144 kg - 0.176 kg per liter and with 0.3-0.63 cm pores, about. 0.9 g ZrH2 per 100 g of the alloy, for a foam product weighing 0.176 kg - 0.277 kg per liter and with 0.15 - 0.3 cm pores, about. 0.6 g ZrH2 per 100 g of alloy, for a foam product with an eh weight of 0.241 - 0.288 kg per litres, and with 0.3 - 0.079 cm pores. The addition can be continued while stirring, e.g. 100 - 3000 rpm. and after the entire amount of foaming agent has been introduced, the stirring speed is increased to 6,000-10,000 rpm. (6) In practice, the foaming process can be carried out in a mold whose internal surfaces limit the shape of the foam-shaped product. The mold can be open or closed as desired. When an open mold is used, the top surface of the product will usually have an irregular shape. When the mold is closed, all excess fat of the foamed product will be confined by the mold and usually there will be less amount of blow holes or large pores.

When a charge foaming process is carried out, there will not be much time between the addition of the foaming agent and the formation of the gas, especially if the temperature of the mass to be foamed is relatively high. This means that to disperse . the foaming agent evenly, rapid dispersion must take place. This can be achieved by stirring at a high speed, which can possibly be achieved by using impact plates in the mixing vessel. As indicated above, it is preferable that the temperature of the molten metal is relatively low so that the blowing gas is not expelled from the blowing agent at such a rate that good foaming is inhibited.

Good foam products can be produced by application

of the method according to the invention. For the production of particularly excellent foam products using this work technique, the following five points should be given as guidelines: Firstly, it is preferred to thicken at a temperature within a certain range above the melting temperature as stated above. The processing temperature must be fairly constant in the metal mass being processed. For up-

achieving the best results, in other words, there should not be a variation of the temperature greater than e.g. 150°C

in the entire mass of the molten metal that is thickened. In view of this, it is preferred that the molten metal has more or less reached equilibrium before the addition of the thickener.

To achieve the best results, attention must be paid to a good mixing technique. M.ao. is determined

not the size of the mixing vessel just based on the capacity requirements,

but it is chosen so that it can be used satisfactorily with the mixing equipment used.

In order to utilize the viscosity-increasing agent in a satisfactory manner, a good mixture is used. What is preferred is to use a mixing technology in such a way that the entire mass of the metal melt being treated is moved or stirred. We have found that an effective stirring technique is satisfactory. For this, it is preferred to use stirring equipment that is effective at high viscosities, e.g. 10,000 - 30,000 cP. We have found a so-called "Cowles Dissolver" or a "Premier Hi Vis Dispersator" with its high viscosity mixing maximum to be satisfactory. When the viscosity-increasing agent is mixed, mixing times are used as stated above.

The addition of the foaming agent is usually carried out by

a temperature which is lower than for the addition of the viscosity-increasing agent. In most cases, it is thus preferred to cool the viscous melt before the addition of the foaming agent. In many cases, the cooling is best carried out in another vessel, i.e. a vessel other than the hot chamber in which the viscosity is increased.

The walls of the second vessel are preferably preheated to within _+ 50°C, preferably +_ 20°C, of the foaming temperature to be used. The viscous material is then added and it is allowed to assume this temperature.

The foaming temperature is somewhat dependent on the viscosity

of the molten mass. For such masses which are particularly viscous, relatively low temperatures can be tolerated and such are preferred. Lower temperatures are used for less viscous materials. As the presence of magnesium increases the viscosity, the foaming temperature will depend to some extent on the magnesium concentration. When a 1.2% by weight magnesium alloy is used, temperatures of approx. 650°C optimal. For aluminum alloys with 2.2 and 7% by weight of magnesium, the optimum temperatures for the addition of the blowing agent are approx. 635 or 615°C.

Certain aluminium-silicon alloys are distinguished by having greater fluidity than pure aluminium. For these alloys, temperatures of approx. 530-570°C, when the blowing agent is added. As with other alloys, e.g. Al-Mg, higher temperatures can of course be used if the fluidity is compensated by the addition of more thickening agent, such as CC^ •

When the foaming agent is dispersed in the mass to be foamed, it is best to aim for a rapid mixing which will produce more homogeneous foam. It is therefore preferable to use a high-speed mixing technique that quickly disperses the blowing agent throughout the molten mass. Mixing considerations related to the above are therefore used when the addition of the viscosity-increasing agent is to be carried out.

After the addition of the leavening agent, the mass is allowed to set

to form foam. This can be done in different ways, e.g. in an open form or a closed form. If the foaming takes place in an open form, the free surface of the foamed mass may take on an irregular shape. When the foaming is performed in a closed mold, the resulting foam product can assume the shape defined by the mold.

For most purposes, the size of the foaming chamber must naturally be sufficient to accommodate the expanding mass. The temperature of the vessel's side walls (in which the foaming takes place) should not be too low. If the temperature is too low, an unwanted thick unblown skin or layer may form. If the tub's side walls are too hot, unwanted large holes can form on the foamed surface. By appropriate regulation of the mold temperature, e.g. the smoothness and thickness of the surface of the finished article is regulated.

If a substantial correspondence between the foamed product and the size and shape of the reaction vessel is of critical importance, precautions must be taken to evenly distribute the foaming mass in the mold. In such cases where the mixing of the foaming agent and the alloy does not take place in the mold where the foaming takes place, it must e.g. precautions are taken to add the mass in such a way that it best complements the shape. The form can e.g. moved to get the mass into the front corners.

The form must not be cooled too suddenly, otherwise the foam product will not be smooth.

Example I

A sample of a magnesium-aluminum alloy with 7 wt% magnesium and 0.2 wt% Mn and weighing 3173 g was melted. Nitrogen gas was at a flow rate of .8 l/min. bubbled through the molten alloy for 5 min. The nitrogen was introduced into the molten alloy through a ceramic tube approximately 5 cm below the surface. The alloy was stirred at approx. 2500 rpm during nitrogen introduction. The stirring was started when the alloy had a temperature of 670°C and at the end of the nitrogen introduction the temperature was 550°C.

The alloy was heated to 725°C and transferred to a treatment furnace. The increase in viscosity which could be observed at the end of the 5 minute run-in period was still evident when the temperature of 725°C was reached. The alloy - before the introduction of nitrogen - had a real viscosity of approx. 31.8 cP, when the temperature 725°C was reached, the viscosity was approx. 29 cP. However, the alloy was very resistant to flow.

The above procedure was repeated using another charge of the alloy weighing 3185 g. The nitrogen flow rate was 7 l/min. and the nitrogen introduction time was 5.4 min.

The two chargers were combined in a crucible heated to 670°C. The metal mass was allowed to cool to 680°C. The mass was stirred at 6,000-10,000 rpm and 40 g of zirconium hydride, ZrH 2 / was added over an introduction period of 8.6 sec. It was then cast into a mold. The mold capacity was approx. 8-9 times the volume of the unopposed liquid united chargers.

The mixture foamed up so that it filled the closed mold. A section was made of the resulting foam product which showed a fine-pored, fairly uniform structure with a volume weight of approx. 0.4 kg/litre (a volume weight of approx. 15% of the non-foamed alloy)'.

Similar results are obtained when the amount of nitrogen used is from 40-60 1/3000 g of alloy. Similar results are obtained when these quantities of nitrogen are introduced over a period of from 2

to approx. 5 minutes. Similar results are obtained when the nitrogen gas is introduced into the alloy at temperatures of from 650 to 710°C. Similar results are obtained when alloys with from 1.2 to 35% by weight of magnesium, silicon or tin are used. Similar results are obtained when from 0.2 to 1.0 g of TiH2, ZrH2 or HfH2 per

100 g of the metal alloy.

When the nitrogen gas was introduced into the molten alloy, white smoke could be observed above the alloy. In addition, the stirrer shaft, which is exposed to this atmosphere, was coated with a fine powder which, on analysis, proved to be magnesium oxide. This formation of magnesium oxide is not observed when carbon dioxide or air is used as the viscosity-increasing agent. It is obvious that the nitrogen does something. magnesium into the atmosphere which reacts with the oxygen in it so that the white smoke is formed.

Example II

This procedure was carried out with 3 charges of an aluminium-magnesium alloy with 7 wt% magnesium and 0.2 wt% Mn.

Charge (a) of said alloy (3130 g) was heated to 715°C. Using a hollow tube shaft and good mixing, argon was introduced into the molten alloy. The argon introduction rate was 16 l/min, and the total time for the argon flow was 3 minutes. The argon introduction cooled the alloy to 604°C. The alloy was very resistant to flow. This substantial reduction in fluidity was also evident after heating the alloy to 704°C.

Charge (b) of said alloy, 1430 g, was melted and heated to 704°C. Through the hollow stirring shaft, 16 l/min. argon introduced for 2 minutes. This introduction of argon cooled the alloy to 649°C. The high viscosity noted was still present upon reheating the alloy to 738°C.

Charge (c) of said alloy, 1730 g, was heated to 715°C and under effective stirring, 16 1 argon/min. introduced through the hollow stirrer shaft for 2 min. This cooled the melt to 682°C and at this temperature the melt was very viscous.

All three charges of the viscous alloy were united in

a crucible which was held at 730°C. The metal was allowed to cool to 685°C. At this temperature, 40 g of ZrH2 was added and it was quickly dispersed for 6.7 seconds.

The thickened mass was transferred by gravity into a 38 x 38 x 11.5 cm mold. (The mold temperature was approx. 300°C.)

The thickened mass was too viscous to flow

well by gravity into the mold, only approx. 85% of the mass therefore reached the form.

The mold was closed with a lid. It was held for 5 min. at 300°C and then removed from the mold chamber. The foamed molded body was removed from the mold.

Production of cross-sections showed that the casting was essentially a smooth, finely pored foam product with a volume weight of approx. 0.29-0.32 kg/l.

Similar results are obtained when 1-4 g of argon is used

per lOOg molten alloy and when used from 0.6

to 1.2 g ZrH2 per said amount of alloy. Similar results are obtained when argon is introduced over a 1-4 minute period and the alloy ring temperature is from 660-710°C.

Example III

One. A 2265 g sample of the same alloy used in Example II was heated to 705°C. With exclusion of air and stirring, 11 liters of nitrogen/min. were introduced into the molten mass for 5 minutes. (The nitrogen was introduced through a hollow stirring shaft using a stirring speed of 2000-3000 rpm). The melt was still very viscous when reheated to 750OC.

Example IV

A sample of 2120 g of the same alloy used in Example III was heated to 705°C. While stirring with a stirrer with a hollow stirrer shaft, - a speed of 2000-3000 rpm - argon gas was introduced into the molten mass through the shaft at a speed of 16 l/min. The argon introduction was carried out at this rate for 5 min.

The gas flow reduced the temperature of the mass to 650°C and greatly increased the viscosity of the molten metal. A high viscosity increase was still evident when the molten alloy was reheated to 760°C.

Example v

A 32 35 g sample of a 7 wt% aluminum alloy

Mg and 0.2% by weight Mn were heated to 705°C and 28 g of CG₂ gas was introduced into the molten mass during 2.5 min. The CG^ addition was carried out under vigorous stirring and the CG^ was introduced through a copper immersion tube. The lower 5 cm of the dip tube eroded during addition. The temperature of the molten metal was reduced to 640°C during the gas supply and the viscosity of the molten alloy increased significantly.

Another sample of the alloy, 3225 g, was heated to 705°C and treated with gaseous CC>2 • This time approx. 7.5 cm of the immersion tube dissolved in the melt. The C02 that was added was 85 g and the addition time 2.7 min. (The dissolution of copper may be the cause of the large amount of C02 required to thicken this charge.) The viscosity was distinctly high and the temperature of the melt

tur dropped to 595°C during the CO2 addition.

The two charges of the viscous melt were combined in a mixing crucible which had a temperature of 670°C. When the metal mass had reached a temperature of 685°C, 40 g of ZrH 2 were added under efficient stirring at 6000 to 10,000 rpm. (During the addition of ZrH 2 , a mechanical accident occurred during which the stirring shaft fell into the mixing crucible.) Nevertheless, the hydride-dispersed metal alloy was transferred by gravity to a 38 x 38 x 11.5 cm mold, the mold being held at 575°C. Due to the high viscosity, the gravity feed to the mold was poor - a large part of the viscous melt was retained. Only approx.

85% of the mold was therefore filled.

A very fine-pored uniformly foamed cast product with a volume weight of 0.4 kg/litre was obtained after cooling and opening the mold.

Similar results can be achieved when using from 0.5-6.0 g C02 per every 100 g of alloy. Similar results are obtained when the same amounts of solid (finely divided) or liquid CO 2 are used at 700-760°C. Similar results are obtained when the alloy to be foamed contains from 1.2-35% by weight of magnesium, silicon or tin. Similar results are obtained when CO2 is added at a temperature of from 20-90°C above the melting point of the alloy. Similar results are obtained when the amount of the ZrH2 foaming agent is from 0.6-1.2 g per 100 g of alloy at 650-705°C.

Example VI

A 3355 g sample of an aluminium-magnesium alloy containing 7 wt% Mg and 0.2 wt% Mn was heated to 715°C.

Under effective stirring, air was introduced into the alloy for 3.5 min. with a speed of 16 litres/min. This greatly increased the viscosity of the molten metal, while the temperature dropped to 625°C. A marked increase in viscosity was still present when the molten alloy was heated to 725°C.

Another 1260 g charge of the same alloy was heated to 680°C. With effective stirring, air was added to the alloy at a rate of 15.5 liters/min. This reduced the temperature to 570°C, and the viscosity increased greatly.

Using a mixing crucible at 695°C, the united charges of viscous alloy were brought. to. a temperature of 679°c and foamed with 30 g of ZrH2- The hydride was mixed in

in

during 5.1 sec. with efficient stirring.

The hydride-treated melt was introduced in a form as indicated in the previous examples. A foamed casting product was obtained that was finely pored and very smooth.

Similar results are obtained when the amount of air is from 0.5-3 g per every 100 g of the alloy. Similar results are obtained when the alloy contains from 1.2 to 35% by weight of magnesium, silicon or tin. Similar results are obtained when the air is mixed at a temperature of from 20-90°C above the alloy's melting temperature. Similar results are obtained when the amount of zirconium hydride is from 0.6-1.2 g per 100 g of the alloy and when the hydride is added at 670-705°C

Example VII

A 1500 g sample of an aluminum alloy with 7.5 wt% magnesium and 0.2 wt% manganese was heated to 690°C. With effective stirring, 90 ml of H 2 O was added to the molten metal over a 5 minute period. The water was added while the temperature of the metal was 675-705°C.

The water increased the viscosity of the melt. The melt was transferred to a crucible at 610°C and just before foaming the crucible temperature was heated to 690°C. 10 g of zirconium hydride was quickly added with efficient stirring at 4500-6500 rpm.

The hydride-treated melt was allowed to foam in the mixing crucible to give a finely pored foam product.

Similar results are obtained when from 1-6 g of H 2 O and 0.6-1.2 g of zirconium hydride are used for every 100 g of the alloy which contained 1.2-35 wt% of silicon, tin or magnesium when added at a temperature of 20-90 °C above the alloy's melting temperature and when ZrH2 is added at 670-705°C.

Example VIII

Using 1627 g of one alloy which contained

7% by weight of magnesium and 0.2% by weight of manganese, the following experiment was carried out.

The alloy sample was heated to 740°C and made viscous with CO2 (solid). The thickened material was transferred to a mixing crucible at 690 C and with vigorous stirring 20 g of HfH2• A few minor detonations took place. The sample was allowed to foam in the mixing crucible.

Claims (3)

1. Process for the production of a solid, shaped product from a foamed metal consisting of aluminum alloyed with at least 1.2% by weight, preferably 2-35% by weight, magnesium, silicon or tin, where a thickening agent is mixed with the molten alloy and then a thickening agent, such as a hydride of zirconium, hafnium or titanium is added, after which the alloy is allowed to solidify, characterized in that a thickening agent is used which is normally gaseous under the working conditions and consists of oxygen, carbon dioxide, nitrogen, air, water or an inert gas such as argon. 2. Method as stated in claim 1, characterized in that from 0.25 to 6.0 g of the thickener is used per 100 g of the alloy. 3. Method as stated in one of the preceding claims, characterized in that the molten alloy is mixed with the thickening agent at a temperature of from 20 to 90°C above the melting point of the alloy.