AT503854B1 - MAGNESIUM-BASED ALLOY - Google Patents

Description

2 AT 503 854 B1

The invention relates to a magnesium-based alloy and a semifinished product produced therefrom.

In more detail, the invention relates to a magnesium-based alloy with uniformly small grain size and high in particular Kaltumformvermögen the material.

Magnesium is an alkaline earth metal, crystallized in hexagonal close packing of the atoms, has a density of 1.7 kg / dm3, a modulus of elasticity of 44 kN / mm2 and a tensile strength of 150 to 200 N / mm2. A hexagonal close-packed lattice has only a limited number of slip planes, so magnesium can only be deformed to a small extent at room temperature.

Alkaline earth metals are generally very reactive. Magnesium is coated in air or water with a thin, adherent, oxide / hydroxide topcoat and is at least partially resistant to especially water. However, despite the protective surface layer, the high reactivity of magnesium may cause corrosion.

To increase strength, reduce notch sensitivity and improve corrosion resistance, magnesium may be predominantly alloyed with the elements aluminum (Al), zinc (Zn), manganese (Mn), these alloys generally being multiphase in the form of mixed crystals and intermetallic phases at room temperature available.

Solution heat treatment followed by quenching can influence the toughness or ductility and, by slow cooling or precipitation hardening, the strength of the material consisting of these alloys.

The most important currently used magnesium alloys have a name and chemical composition listed in Table 1.

However, known magnesium alloys have the disadvantages of an inhomogeneous structural adjustment in the bolt during extrusion at elevated temperature and a limited ductility of the material at room temperature.

A major advantage of magnesium is in particular the low density of the metal, so that for a long time the professional world has been confronted with the desire for magnesium-based wrought alloys.

From a publication "The Effect of Ca Addition on Age Hardening Behaviors and Mechanical Properties in Mgb-Zn Alloy" (Materials Science Forum Vols. 419-422 (2003) pp. 307-312), for example, it has become known an alloy of To add magnesium and 6 wt .-% zinc, 0.1 to 0.5 wt .-% calcium in order to increase the mechanical properties and improve the curing parameters.

With the same objective of increasing the firmness and improving the creep resistance, according to the document "Microstructure and mechanical properties of Mg-Zn-Si-based alloys" (Materials Science and Engineering A357 (2003) 314-320), alloying of 1% by weight was carried out. Si and optionally 0.25 wt .-% Ca a magnesium base material with 6 wt .-% Zn.

In order to provide high strength and deformed magnesium base alloys, it has also been attempted as disclosed in the document "Microstructure and Mechanical Properties of Mg-Zn-Ag Alloys" (Materials Science Forum Vols. 419-422 (2003) pp. 159-164) to add silver (Ag) to a Z6 alloy, wherein with a content of 3% by weight Ag, a remarkable grain refinement and a hardness increase could be achieved.

The invention is now the goal of creating a magnesium-based alloy, which produces a fine-grain billet in a hot pressing an optionally conditioned continuous casting bolt, the material of which is highly deformable at elevated temperature and at room temperature. It is a further object of the invention to improve or to influence the corrosion resistance of the material.

However, this goal is achieved with a magnesium base alloy containing but less than 6.2 in weight percent but less than 1.0 but less than 1.0 but less than 1.0, but less than 1.0 but less than 0.5 but less than 2.0

Silver (Ag) Magnesium and manufacturing impurities are reached as the remainder.

Zinc (Zn) zirconium (Zr) manganese (Mn) calcium (Ca) silicon (Si) antimony (Sb) aluminum (AI) more than 0.8, traces, more than 0.04, more than 0.04, traces, Tracks, tracks, more than 0.1,

The advantages achieved with the magnesium base alloy according to the invention are essentially in a strictly balanced element concentration and a microalloying technology, in which the interaction of all alloying elements and the reaction kinetics and grain growth criteria are taken into account, the advantages, in particular a homogeneous fine grain structure of the material, a high Cold formability and improve the corrosion resistance of the same represent.

Zinc at levels greater than 0.8 to less than 6.2 weight percent in the alloy significantly affects the solidification interval and prevents formation of very coarse columnar crystals upon solidification. Lower concentrations than 0.8% by weight of Zn lead to a disproportionately decreasing effect, whereas contents of more than 6.2% by weight result in a disadvantageously acting eutectic solidification of the melt.

Zirconium is fine-grained by precipitations from the melt and enrichment at the crystallization front. Contents of more than 1.0 wt% Zr coarsen the precipitates in for the crack initiation of the material under adverse conditions.

Manganese at levels greater than 0.04 but less than 0.6 weight percent has a multiple effect in the alloy. On the one hand, Mn binds in the melt Fe, which compound precipitates, on the other hand Mn forms with zirconium even at a higher temperature in the melt phases, which can have a fine grain.

Calcium at levels greater than 0.04 but less than 2.0 weight percent in the metal provides phase formation in the solid alloy, which phases as a grain boundary stabilizer effectively hinder crystal growth. This Ca2Mg6Zn3 phase, which presupposes Zn in the above-mentioned contents in the alloy, is produced in the range from 0.1 to 1% by volume, particularly finely and homogeneously distributed in the material, whereby an outstanding fine grain structure is retained in the material.

Grain boundary stabilizing precipitates in conventional magnesium alloys are generally more noble than the magnesium matrix, so that the corrosion resistance is impaired by galvanic effects. In the alloy according to the invention, the base Ca2Mg6Zn3 phase precipitates, so that a galvanic corrosion mechanism is significantly reduced. The result is improved corrosion resistance.

The alloying element silicon is soluble in magnesium only to a very small extent or in traces and forms the phase Mg 2 Si. About 1.0 wt .-% Si is the phase fraction in the factory

Alloy material large and deteriorates its mechanical properties.

Antimony is essentially related to silicon because antimony can provide a modification of the Mg 2 Si phase, with a required Sb concentration in the alloying metal being about half of that of Si.

Although magnesium-based alloys, which may contain up to 8 wt .-% aluminum and above, also have an application potential in terms of increased material strength and creep resistance, aluminum is an undesirable element in the material according to the invention. By contents of greater than 0.5 wt .-% can arise brittle grain boundary phases of the type Mg17AI12, which also act in a coarse formation of corrosion. Furthermore, during the extrusion of the material below about 230 ° C cracks, which can lead to a brittle pressing, which may also have significant grain size differences over the cross section and the longitudinal direction.

Silver has a high potential as a grain growth inhibiting element in the alloy according to the invention in the contents of more than 0.1, but less than 2.0 wt .-%. Ag is in these concentrations in the warm state of the alloyed material in solution, which was found at levels of about 0.1 wt .-% Ag an increase in concentration at the grain boundaries is formed, which highly effectively precludes grain growth. Furthermore, a hardening effect of the material over the Mg4Ag phase can be achieved by Ag. Higher Ag contents than 2.0% by weight have, in particular, economic and corrosion-chemical disadvantages.

In claims 2 and 3 preferred chemical compositions of the magnesium-based alloys according to the invention are given.

Of particular importance for a homogeneous fine-grained microstructure and a high deformability of an article of the alloy according to the invention in the range of room temperature, it was found, the sum concentration of the micro-alloying elements Mn, Ca and Si of greater than 0.1, but less than 0.65 Wt .-% in the magnesium base material.

A semifinished product of a magnesium-based alloy according to the invention, which has been deformed with a cross-sectional area ratio of greater than 1:16, in particular greater than 1:20 of a cast bolt to a pressure at a temperature of about 380 ° C, has a Grain size of the structure of less than 10 pm, and with a high degree of isotropy in relation to the cross section and in the longitudinal direction. Inventive compacts can be further deformed or pressed at temperatures below 200 ° C, in particular at room temperature, with an error-free surface or gloss surface can be achieved.

The invention will be substantiated below with some experimental results.

Tab. 2 gives the chemical composition of the investigated materials.

The figures show:

Fig. 1 Stress-strain behavior of tested alloys Fig. 2 Experimental alloy L1 \ cast structure Fig. 3x Test alloy L1, cast structure

Fig. 3.1 Magnification scale: 500 pm Fig. 3.2 Magnification scale: 200 pm Fig. 3.3 Magnification scale: 50 pm Fig. 3.4 Magnification scale: 20 pm Fig. 4x Test alloy L1 deformed 5 AT 503 854 B1

Fig. 4.1 Cross-section edge Fig. 4.2 Cross-section center Fig. 4.3 Longitudinal section edge Fig. 4.4 Longitudinal section center Fig. 5 Test alloy L2, cast structure Fig. 6x Test alloy L2, cast structure

Fig. 6.1 Magnification scale: 500 μηπ Fig. 6.2 Magnification scale: 200 μηη Fig. 6.3 Magnification scale: 50 pm Fig. 6.4 Magnification scale: 20 μπι Fig. 7x Trial alloy L2

Fig. 7.1 Cross-section edge Fig. 7.2 Cross-section center Fig. 7.3 Longitudinal section edge Fig. 7.4 Center longitudinal section Fig. 8 Comparison alloy AZ31, cast state Fig. 9 Comparative alloy ZK31, cast state

Fig. 1 shows the result of the elongation as a function of the tension in the tensile test according to EN 10002-1: 2001 of magnesium-based alloys.

In the following, reference will be made to the alloy designations and alloy compositions given in Tab.

The sample labeled L1 of an alloy according to the invention with deformation by indirect pressing and with a compression ratio of 1:25 yielded an elongation of more than 25% at room temperature in the tensile test (A50) at a maximum stress of about 260 MPa.

On the sample of a further trial alloy L2 according to the invention, a yield strength of Rp0.2 = 330 MPa of the material was determined at 380.degree. C. at room temperature using an elongation value of greater than 15% in the case of ductility given case of about 19%.

The comparative alloys ZK31, AZ31 and ZM21 had, as is apparent from Fig. 1, consistently lower elongation at break Ac than the materials of the invention.

From Fig. 2, the dendritic cast structure of alloy L1 can be seen. An average particle size of 140 μm was determined with a substantially homogeneous structure over the entire cross-section of the block.

3 shows the largely homogeneous microstructure in the cast state of the block of the alloy L1 over the cross section in with different magnifications at a scale of 500 μm (FIG. 3.1), 200 μm (FIG. 3.2), 50 μm (FIG. 3.3). and 20 μηη (Figure 3.4) and shows spherical grains with some grain boundary phases.

FIG. 4 shows a material of the alloy L1 according to the invention, deformed at a press ratio of 1:25 at 380 ° C., in the longitudinal and transverse direction from the edge and middle regions of the sample.

Figures 4.1 and 4.2 are cross-sectional images of the edge and the center of the rod, with Figures 4.3 and 4.4 illustrating the corresponding longitudinal section images. An average particle size of 9 pm to 6 pm was measured.

FIG. 5 shows the globulitic cast structure of an alloy L2 according to the invention. 6 AT 503 854 B1

With largely homogeneous particle size distribution over the cast block, the mean particle size was 40 μm.

Fig. 6 shows the cast structure of Fig. 5 (L2) in its highly fine form with scale of 500 pm (Fig. 6.1), 200 μιτι (Fig. 6.2), 50 μιτι (Fig. 6.3) and 20 μπι (Fig 6.4). There are small fine precipitation phases at the grain boundaries.

FIG. 7 shows the structure of a compact of an alloy L2 of a cast block pressed at a temperature of 380 ° C. with a press ratio of 1:25 in the transverse direction at the edge (FIG. 7.1) and in the center region (FIG. 7.2) and in the longitudinal direction at the edge (Fig. 7.3) and in the central region of the rod (Fig. 7.4). The mean grain size was about 2 pm.

The cast structure of a block of a comparison alloy AZ31 is shown in FIG. 8. A measurement of the microstructure resulted in a grain size of 360 μm with a substantially homogeneous distribution over the cross section.

After extruding at 380 ° C, the microstructure was partially coarsely recrystallized and inhomogeneous, whereby no secured grain size determination was possible.

As shown in Fig. 9, the cast structure (chill casting) in the block of the comparative alloy ZK31 was globulitic and had a grain size of 80 μm with good homogeneity across the cross section.

After a hot pressing of the cast bolt, the extruded profile was partially inhomogeneously recrystallized. A crystal size determination with a certain significance was not possible at the press profile.

Tab. 1: Compositions of magnesium alloys according to the prior art (in% by weight)

Alloy designation Zn Mn Al Si Ca Zr Mg Z 6 6.0 Rest ZM 21 2.0 1.0 Rest ZK 31 3.0 0.6 Remainder AZ 91 * 0.8 0.4 9.0 max. 0.5 remainder AM 60 * 0.25 6.0 remainder AZ 31 1.0 to 1.0 3.0 remainder * mainly cast alloys

Tab. 2: Compositions of tested materials (in% by weight)

Alloy designation Zn Mn Al Si Ca Zr Ag Mg L 1 2.9 0.2 - 0.2 0.5 Rest L 2 2.8 0.1 - 0.2 0.8 0.4 Remainder ZM 21 ** 1.8 0.7 remainder CC 31 ** 2.7 0.5 remainder AZ 31 1.0 0.3 3.0 remainder

Claims (4)

7 AT 503 854 B1 ** no standard alloys Claims: 1. Feinkom magnesium base alloy containing in% by weight zinc (Zn) zirconium (Zr) manganese (Mn) calcium (Ca) silicon (Si) antimony (Sb) silver ( Ag) greater than 0.8, traces, greater than 0.04, greater than 0.04, traces, traces, greater than 0.1, optionally aluminum (AI) but less but less, but less, but less, but less less than 0.5 mg and manufacturing impurities than 6.2 as 1.0 as 0.6 as 2.0 as 1.0 as 0.5 as 2.0 remainder. 2. Magnesium base alloy according to claim 1, in which the micro-alloying elements Mn, Ca, Si have a sum concentration of greater than 0.1, but less than 0.65, preferably greater than 0.15, but less than 0.5. The magnesium base alloy according to claim 1 or 2, wherein the concentration in wt% of one or more alloying elements Zn is more than 1.0, preferably more than 1.5, but less than 5.9, preferably less than 4 , 0 Zr less than 0.8, preferably less than 0.6 Mn more than 0.06, preferably more than 0.09 but less than 0.4, preferably less than 0.2 Ca more than 0.1, preferably more as 0.14 but less than 1.0, preferably less than 0.6 Si less than 0.5, preferably less than 0.2 Sb less than 0.25, preferably less than 0.1 Al less than 0.1, preferably less than 0.08 Ag is more than 0.2, preferably more than 0.38 but less than 1.2, preferably less than 0.9. 4. A semi-finished product of a magnesium-based alloy having a chemical composition according to any one of claims 1 to 3, deformed with a pressing ratio of at least 1:20, which semi-finished product has a particle size of less than 10 pm and has extensive isotropy. Including 8 sheets of drawings