AT511207B1 - ALUMINUM ALLOY WITH SCANDIUM AND ZIRCON - Google Patents

Abstract

Aluminum alloy for die casting, containing silicon: 1.5 to 3.0% by weight, manganese: 0.3 to 0.8% by weight, magnesium: 4.5 to 6.5% by weight, scandium and zirconium: together 0.2 - 0.65 wt .-%, production-related impurities, and balance aluminum.

Description

Austrian Patent Office AT511 207B1 2012-10-15

Description: The invention relates to aluminum alloys for die-casting for producing high-strength parts for the automotive and aircraft industries. For such parts not only the highest tensile strength is required, but also a number of other properties: high yield strength and elongation at break, good weldability and corrosion resistance, and also high ductility (high energy absorption in plastic deformation). Because such parts often have complicated shapes and are as thin as possible to weight savings, good mold filling capacity and robust cooling behavior is required. For reasons of cost and because of possible distortion of the workpiece as simple as possible, if at all possible, no thermal aftertreatment of the castings is desirable.

[0002] From the data sheet "Cast material MAXXALLOY 59 " Salzburger Aluminum Group is well-known for diecasting aluminum alloy containing 5-6% magnesium, 0.5-0.8% manganese, 1.8-2% silicon, and a maximum of 0.07% zinc, 0.02% Copper, 0.15% iron and 0.05 - 0.15% titanium. This alloy achieves excellent mechanical properties even without heat treatment and is corrosion resistant and excellent weldability. For certain applications, however, an even higher tensile strength and ductility is desired.

WO 2006/127812 discloses a high-strength cast aluminum alloy which has the following alloying elements: 1.0-4% magnesium, 4-9% zinc, 1- 2.5% copper, maximum 5% manganese, at most 0.1 or 0.12% silicon and iron, 0.1-0.5% scandium, 0.02-2% zirconium, and some more boron and titanium. Increasing the tensile strength serves here the increased content of copper and zinc. Magnesium favors high and thermally stable hardness, weldability and corrosion resistance. A disadvantage is the high content of zinc, which is detrimental to corrosion resistance, significantly reduces the toughness (ductility) and requires a complex heat treatment.

EP 918095 A1 discloses an aluminum alloy suitable for die casting. It contains only 0.1-0.8% silicon, 0.5-0.8% iron, 1.2-1.4% manganese, at most 1.5% magnesium and 0.2-0.4% scandium, 0.1-0.4% zircon, no copper and only a little zinc. However, the relatively high proportion of manganese and iron increases the proportion of intermetallic phases (AlMnFe). Although this alloy is characterized by high ductility, its strength values (yield strength (Rp0.2) and tensile strength (Rm) leave much to be desired and can be improved by careful heat treatment, but at the expense of ductility.

It is therefore an object of the invention to further improve the above quoted in the first place alloy while maintaining their good properties in terms of tensile strength, mold filling and ductility, especially for low wall thickness and in view of higher wall thickness higher risk of distortion as possible without thermal treatment.

According to the invention, this is achieved with an aluminum alloy for diecasting, containing [0007] silicon: 1.5 to 3.0% by weight, [0008] manganese: 0.3 to 0.8% by weight, [0009] magnesium: 4.9 to 6.5% by weight, scandium and zirconium together: 0.2-0.65% by weight, [0011] production-related impurities, and [0012] - Rest aluminum.

The content of silicon of 1.5 - 3.0% causes excellent casting and welding properties and the corrosion resistance benefits, but is held in this area to hold negative effects (increase in hardness, hot cracking hazard) behind and without heat treatment get along. The content of manganese is limited to 0.8%, in which 1/8 Austrian Patent Office AT511 207 B1 2012-10-15

Concentration he already causes an increase in the strength and the recrystallization temperature, but the low solubility of manganese in aluminum takes into account. The 5.0-6.5% relatively high content of magnesium benefits the hardness without the need for a special heat treatment, and does not decrease by welding.

Scandium or scandium and zirconium, which are present together to 0.2 to 0.65%, both act fine grain (thereby no hot cracking tendency), cause on curing mixed phases (AI3Sc and / or AI3Zr), which contribute significantly to the increase in strength , and further cause a shift in the recrystallization temperature to much higher temperatures. As a result, a subsequent heat treatment is unnecessary in most cases. All it takes is a cold outsourcing. Scandium leads to a change in the morphology of the structure from dendritic to globulitic, which illustrates the advantages mentioned. The production-related impurities are, for example, iron, copper and zinc.

Preferably, the alloy contains a total of 0.28 to 0.33% scandium and zirconium. They provide the optimum for tensile strength, ductility and other properties. The higher values in claim 1 apply if the tensile strength-reducing effect of magnesium is to be compensated for in extreme load cases.

Although scandium and zirconium partially exert the same influence on the alloy, the ratio of scandium to zirconium such as 1.5 to 2.5 to 1 is particularly favorable. For thinner to thinner wall thicknesses, the optimum is at a content of 0.12 to 0.25% of scandium and 0.08 to 0.13% of zirconium.

The production-related impurities are each limited to 0.2%. In particular, the content of iron and zinc should each remain below 0.1%. Iron is usually present in small amounts anyway in aluminum, should not exceed 0.3% significantly, because about 0.5% form in the structure of brittle needles that affect the ductility. Titanium is very fine in very small amounts (0.3% optimum) and dramatically reduces crystal lattice misfit. The content of zinc is kept small because more zinc is detrimental to corrosion resistance.

In the following the invention will be described and explained with reference to figures. In the drawings: Fig. 1: Fig. 2: Fig. 3: Fig. 4: [0022] Fig. 4:

Table of the measured values of tensile strength, yield strength and elongation at break of the tested alloys;

Micrograph of a reference alloy;

Microsection of a first alloy according to the invention; and

Microsection of a second alloy according to the invention.

In the present disclosure, all percentages (%) are by weight (% by weight) unless expressly stated otherwise.

To assess the effect of the proportions of certain alloying elements and their optimization, a number of alloy compositions on a die casting machine (Buehler SC D / 53) was poured. Was rinsed with argon. As samples stepped plates with gradually increasing wall thickness of 1.8; 3.0; Poured 4.7 and 6.9 mm. Tensile tests and a microstructural examination were carried out on the step plates, and a spectral analysis was carried out to check the chemical composition and micrographs.

The following alloy compositions were tested in the above manner: Silicon: Mn: Magnesium: 1.5 to 1.9 wt%, 0.6 to 0.7 wt% , 4.9 to 6.5 wt .-%, 2/8 Austrian Patent Office AT 511 207 B1 2012-10-15 wherein the percentage ranges of the scattering of the individual alloys (hereinafter No. 1a, 8, 9 and 10 ) Take into account, further manufacturing-related impurities, balance aluminum. The restriction to alloys 8, 9, 10 is already the result of a selection after preparatory trials. The proportions of scandium and zirconium were varied as follows, where la is a reference alloy without scandium and zirconium:

No. internal No. Sc [wt%] Zr [wt%] Sc + Zr [wt%] 1a Sc_D_107x 0.00 0.00 0.00 8 Sc_D_108x 0.24 0.09 0.33 9 Sc_D_109x 0.18 0.11 0.29 10 Sc_D_110x 0.14 0.13 0.27 The result of the tensile tests on the above 4 alloys, in each case for the 4 zones of different thickness of the step plates, is shown graphically in FIG , The left-hand diagram in Fig. 1 is for a thickness of 1.8 mm, the adjacent right for a thickness of 3.0 mm, the next for a thickness of 4.7 mm and the right outer for a thickness of 6.9 mm. For each alloy and in each graph, three vertical bars are shown next to each other, from left to right the first one for the tensile strength Rm in MPa (megapascal), the second for the elongation at break A as a percentage of the length before the tensile test and the third for the 0 , 2% - yield strength Rp0.2 in MPa. The corresponding scales are entered on the left and right margins.

When comparing the values, it first becomes apparent that the values for the thinnest sample are the best and all values decrease with increasing sample thickness. The alloys of the invention should indeed be particularly suitable for thin-walled parts.

The best mechanical values are achieved with additions of Sc and Zr of 0.29 to 0.33% together, see values of alloys 8 and 9. Specifically, the optimum was 0.24% Sc and 0.09%. Zr (Alloy 8) or 0.18% Sc and 0.11% Zr (Alloy 9).

For alloy 8, a tensile strength up to over 280 MPa and an elongation at break of more than 5.5% were measured. For alloys with optimum proportions of Sc and Zr (alloys 8 and 9), strength and elongation were better than for the reference alloy 1a. It can also be seen that the elongation at break was most affected by varying the addition of Sc and Zr. The influence on the yield strength Rp0,2 was moderate to low.

These results are confirmed by comparison of micrographs produced with the light microscope, which are shown for the reference alloy 1a and the alloys 8 and 9 in Figs. In these, 1 cm corresponds to approximately 200 microns.

The reference alloy 1a still shows largely dendritic microstructure with an average grain size of 90 microns. Alloy 9 shows a dendritic-globular structure with a mean grain size of 50 microns. Finally, alloy 8 is a particularly fine, purely globulitic microstructure with a mean particle size of 23 microns. The particularly fine globulitic structure offers additional advantages beyond the above measured values: high energy absorption during deformation (in vehicle construction in the event of a collision), excellent weldability because largely independent of thermal influences, no susceptibility to hot cracking, corrosion resistance. 3.8

Claims (7)

Austrian Patent Office AT511 207 B1 2012-10-15 Claims 1. Aluminum alloy for diecasting, containing silicon: 1.5 to 3.0% by weight, - manganese: 0.3 to 0.8% by weight, - magnesium: 4.5% to 6.5% by weight, scandium and zirconium together: 0.2-0.65% by weight, impurities due to the production, and balance aluminum. 2. Aluminum alloy according to claim 1, characterized in that it contains 0.28 to 0.33% scandium and zirconium together. 3. Aluminum alloy according to claim 1, characterized in that the proportions of scandium to zirconium behave as 1.5 to 2.5 to 1. 4. Aluminum alloy according to claim 2, characterized in that it contains 0.12 to 0.25% scandium and 0.08 to 0.13% Zr. 5. Aluminum alloy according to one of the preceding claims, characterized in that it contains not more than 0.1% iron. 6. Aluminum alloy according to one of the preceding claims, characterized in that it contains 0.1 to 0.2% titanium. 7. Aluminum alloy according to one of the preceding claims, characterized in that it contains a maximum of 0.1% zinc. 4 sheets of drawings 4/8