NO128333B - - Google Patents

Description

Aluminum casting alloy and method by

manufacture thereof.

The present invention relates to aluminum stop alloys-

which, after heat treatment, is characterized by high mechanical strength,

and more particularly aluminum alloys with high tensile strength, high yield strength and good toughness, as well as methods for producing such alloys.

In recent times, there has been a growing need for aluminum alloys with good mechanical properties for various industrial purposes, such as for example in the car, aircraft and construction industries.

Relatively high strength-é' can be achieved with aluminum stop alloys, but satisfactory strength can hardly be achieved with aluminum stop alloys.

A few aluminum stop alloys with a tensile strength of approx.

^0 kp/mm is already well known, nine alloys with tensile strengths of ^5 kp/mm or more are only known from alloys in the aluminium-zinc-magnesium system.

Alloys containing relatively large amounts of zinc are very susceptible to stress corrosion cracking. Aluminium-copper-magnesium solvo-stop alloys which are described in British Patent Document No. 1'. 090.960, also have high tensile strength of h- 5 kp/mmo or more, but these alloys are very expensive due to the sol content. There has therefore been a need to develop cheap aluminum stop alloys with high tensile strength of ^5 kp/mm or more, and it has also been desirable to develop other mechanical properties.

An alloy is known from British Patent No. 550,516

which consists of 0.5-10 weight percent Cu, 0.5-5 weight percent Mg,

0.5-10 weight percent Cd and the rest Al. The high content of Mg means that the manufactured objects tend to form stop cracks and stress-corrosion cracks. Furthermore, the high content of Mg requires careful monitoring of the heat treatment temperature and the casting process. The present alloys not only have high strength, but also good stope properties.

Al-Cu-Cd alloys are known from British patent document no. 681,906, but the introduction of Mg in the alloy is not used to effectively improve the mechanical properties.

As a result of investigations of aluminum stope alloys with high tensile strength, high yield strength and good toughness, and particularly those that have good resistance to thermal cracking and stress corrosion cracking, it was found that aluminium-copper-magnesium-cadmium stope alloys satisfied the in front of the aforementioned NOK of..... It has been known that the usual aluminium-copper-magnesium alloys have achieved relatively good mechanical properties by heat treatment. The mechanical properties of these alloys can be noticeably improved by the addition of small amounts of cadmium and appropriate heat treatment, i.e. that tensile strength, yield strength and elongation can respectively amount to k- 5 kp/mm 2 or more, M> kp/mm o or more and k - to ^ 0% or more. These mechanical properties can be compared with the properties of the expensive aluminium-copper-magnesium-solv alloys.

The present invention therefore relates to an aluminum stop alloy which, after heat treatment, is characterized by high strength,

and the distinctive feature of the alloy is that it consists of <>>+.0 to 6.2 weight percent copper, 0.2 ti-l 0.^ weight percent magnesium,'0.05

to 0.8 weight percent cadmium, optionally 0.01 to 0.5 weight percent titanium and/or 0.001 to 0.01 weight percent boron and optionally up to 1.0 weight percent manganese and/or up to 2.0 weight percent solv, the remainder being aluminum.

The content of alloying elements in the aluminum stop alloy is determined by the following factors:

Copper addition is essential to increase the strength of the alloy.

Copper in amounts from k-, 0 to 6.2% is required for this purpose. Addition of copper in amounts above 6.2% leads to unwanted

increase in the phase which is soluble in the base mass, even during dissolution heat treatment, and is therefore unfavorable when it comes to retaining the good mechanical properties. Furthermore, the tendency to thermal breakdown increases. For optimal results, copper is added in amounts from h, 7 to. 5.5%.

Magnesium addition increases the alloy's strength and aging properties. Magnesium in amounts from 0.2 to 0, h% is required for this purpose. Addition of magnesium in amounts above 0.5%

increases the tendency to heat fracture and often causes burning and rapid cooling cracks if the temperature for the dissolution heat treatment is high, while the strength decreases if a lower temperature is used for the dissolution heat treatment, thereby preventing heat fracture. For optimal results, magnesium is added in amounts from 0.2 to 0.0%.

Adding a small amount of cadmium to the aluminium-copper-magnesium alloy increases the age-hardening properties and the mechanical properties of the alloy, and also improves the resistance to stress corrosion cracking. Cadmium in amounts from 0.05 to 0.8% is required for this purpose. Addition of cadmium in amounts above 0.8% tends to thermal breakdown,

burning during the dissolution heat treatment and brazing cracks. For optimal results, cadmium is added in amounts from 0.1 to 0.2%. Cadmium is cheaper than sol and therefore this aluminium-copper-magnesium-cadmium alloy can be produced at lower costs.

Titanium is beneficial for ensuring a fine-grained structure in the alloy, good mechanical properties through a successful solution heat treatment to prevent thermal cracking. Titanium in amounts from 0.01 to 0.5% is required for this purpose. Addition of titanium in quantities above 0.5% causes the separation of coarse compounds, and this reduces the mechanical properties. For optimal results, titanium is used in amounts from 0.1 to 0.3%.

Boron in an amount of 0.001 to 0.01% added to the alloy together with titanium in the master alloy or in the fluxes is beneficial, to ensure a fine grain structure.

The alloy's properties are further improved by adding sol and manganese to the aluminium-copper-magnesium-cadmium alloy. The addition of small amounts of solv also increases the age-hardening properties and the mechanical properties of the alloy. That is to say, a tensile strength of 50 kp/mm 2 or more can be achieved, yield strength of !+5 kp/mm 2 or more and elongation from h to 15% - Addition of solv in amounts below 2.0% improves the mechanical the properties. Addition of solv above 2.0%, however, no longer has any effect when it comes to improving the mechanical properties. As solv is an expensive metal, it is preferred that solv is added in amounts below 2.0%. Although the price of the alloy is increased by the addition of solv, the requirement for particularly high strength of stope goods can be achieved by the addition of solv.

The addition of manganese improves the alloy's resistance to stress corrosion cracking. That is to say, the addition of manganese in quantities below 1% increases the resistance to stress corrosion cracking without reducing the mechanical properties, but the addition of manganese above 1.0% has no effect. For

optimal results use manganese in amounts below 0.5%.

It is desirable that aluminum of as high a purity as possible is used for the production of the aluminum-copper-magnesium-cadmium alloys. The iron and silicon content should preferably be below 0.2%. The optimal ranges for the content of alloying elements are as follows:

Copper: <1>+.7-555 percent by weight

Magnesium: 0.2-0, h weight percent

Cadmium: 0.1-0.2% by weight

Titanium: 0.1-0.3% by weight

Boron: less than 0.01% by weight

The aluminum alloy is heat treated in the following way. The dissolution heat treatment must be carried out at a temperature higher than 5'00°C for a period of time sufficient to completely dissolve the copper-rich compound in the base mass. The temperature for the dissolution heat treatment is preferably chosen as high as possible without causing burning or brazing cracks. The upper limit of the temperature is determined by the content of alloying elements, especially cadmium and magnesium. The aluminum alloy of the preferred composition is preferably solution heat treated at 530°C for 12 hours.

Water brazing after the dissolution heat treatment must be carried out as quickly as possible. The temperature of the water after the rapid jolling must not exceed 50°C. The quenching temperature for complicated stop goods with parts of different thicknesses should preferably be lowered 5 to 10°C in relation to the temperature for the solution heat treatment in order to prevent internal stress or breakage during quenching.

The hardening heat treatment of this aluminum alloy is carried out at approx. 160Q to 190°C for <1>+ to ^8 hours.

The maximum strength is achieved by curing at 175°C for 20 hours. The high yield strength is achieved by curing over a longer period of time

a higher temperature, while high elongation, on the other hand, is achieved by curing over a shorter time at a lower temperature.

In the event where. a high extension is required at the expense of the yield strength, the curing temperature should not exceed 160°C.

Example 1.

Aluminum of 99.9% purity is cleaned to remove machine oil and dirt. It was then dried and filled into a graphite crucible and melted. After the temperature in the forge had reached 750°C, an aluminium-5% titanium pre-alloy was added to the forge. Then copper was added to the smelt at 750°C and the smelt stirred. Then cadmium was wrapped in aluminum foil and magnesium added to the smelt at 730°C and 750°C respectively.

Flux containing titanium and boron (KpTiFg + KBF^ + C2C16-)

was then added to the melt at 750°C in amounts from 0.1 .

to 0.2%, on the basis of the forging, for refinement of the grain structure of the alloy. Finally, hexachloroethylene pellets (CgCl^) were added to the melt to degas it.

The resulting melt is held at 750°C for 30 minutes and subjected to a gas evolution test by pouring approx. 200 g melt in. a preheated insulated mold. The melt solidifies under a reduced pressure of approx. 5 nira Hg and evolved gas are observed from the refracted melt.

After determining that there was no more gas evolution from the sample, slag was removed from the surface of the melt and the melt was poured into a permanent sample form. The stop samples were solution heat treated at 530°C for 12 hours, quenched in cold water and cured at 165°C for 32 hours.

The test pieces were subjected to tensile tests and chemical analysis.

Tensile tests: Tensile strength ^8.6 kp/mm, yield strength (0.2% deviation) ^3.6 kp/mm and elongation 6%.

Chemical composition: Cu 5.37%, Mg 0.33%, Cd 0.13%, Ti 0.16%,

B 0.00<*>+%, Fe 0.07%, Si' 0.05%i and the rest aluminum. Example 2. An aluminum alloy melt was produced by the same melting and alloying process as in example 1. Gas in the melt was removed by introducing a gas mixture of chlorine and nitrogen into the melt through a graphite tube. The test pieces that were cast in the mold were quench heat treated at 525°C for 6 hours, quenched in cold water and cured at 180°C for 16 hours. The tensile strength, yield strength (0.2% deviation), elongation and chemical composition ■■ of the resulting alloy were as follows: Tensile strength ^7.0 kp/mm 2 , yield strength ^0.6 kp/mm 2 , elongation 9.6 %. ;Chemical composition: Cu Lf,83%, Mg 0.31%, Cd 0.11%, Ti'0.02%, ;B 0.003%, Fe 0.07%, Si 0.0*+% and the rest aluminum .

The titanium in the alloy was not obtained from aluminium-titanium alloy, but from the flux.

Table 1 shows the chemical composition of aluminum alloys

according to the present invention as well as for known high-strength heat-resistant aluminum stop alloys.

Table 2 shows the dissolution heat treatment conditions and the mechanical properties at room temperature of the alloys indicated in table 1.

Table 3 shows the mechanical properties at elevated temperatures of the alloys indicated in tables 1 and 2.

Tensile strength and yield strength are indicated in kp/mm p.

Elongation is indicated in %.

Tables 2 and 3 show that the aluminum alloys according to the present invention have excellent mechanical properties at room temperature and at elevated temperatures.

As mentioned above, the aluminum alloys can be produced at low cost and still have good mechanical properties compared to aluminum alloys of a known type. They can therefore be used in various types of machine parts, aircraft, rolling stock, building structures and other construction materials.

Claims (3)

1. Aluminum stop alloy which after heat treatment is distinguished by high strength, characterized in that it consists of ^.0 to 6.2 weight percent copper, 0.2 to 0.^ weight percent magnesium, 0.05 to 0.8 weight percent cadmium, optionally 0.01 to 0.5 weight percent titanium and/or 0.001 to 0.01 weight percent boron and optionally up to 1.0 weight percent manganese and/or up to 2.0 weight percent solv, the remainder being aluminum. 2. Alloy as specified in claim 1, characterized in that it contains ^.7 to 555 weight percent copper, 0.2 to 0.^ weight percent magnesium, 0.1 to 0.2 weight percent cadmium, optionally 0.1 to 0.3 weight percent titanium and/or up to 0.01 weight percent boron and possibly up to 0.5 weight percent manganese and/or up to 2.0 weight percent solv. 3. Method for producing an alloy as specified in claims 1-2, with high strength, characterized in that the alloy is solution treated at a temperature higher than 500°C and that the solution treated alloy is hardened at a temperature in the range of 160 to 190°C.