ES2615127T3 - Magnesium base alloy - Google Patents

Abstract

Base alloy of fine grain magnesium compound% by weight of zinc (Zn) more than 0.8, however, less than 6.2 zirconium (Zr) traces, however, less than 1.0 manganese (Mn) more of 0.04, however, less than 0.6 calcium (Ca) more than 0.04, however, less than 2.0 silicon (Si) traces, however, less than 1.0 antimony (Sb) traces , however, less than 0.5 silver (Ag) more than 0.1, however, less than 2.0 mg and impurities due to production as a remainder.

Description

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DESCRIPTION

Magnesium base alloy

The invention relates to a magnesium base alloy and a semi-finished product produced therefrom.

Specifically, the invention relates to a magnesium base alloy with a uniformly reduced grain size and a high capacity, particularly in terms, of the material.

Magnesium is an alkaline earth metal, crystallizes in a spherical packing of the maximum hexagonal density of atoms, has a density of 1.7 kg / dm3, an elastic modulus of 44 kN / mm2 and a tensile strength of 150 a 200 kN / mm2. A densely packed hexagonal net only has a limited set of gliding planes, so that magnesium can only be formed to a small extent at room temperature.

In general, alkaline earth metals are very reactive. Magnesium is coated in the air or in water with a thin, tightly adherent, oxidic / hydroxyphic coated layer and is at least partially resistant, particularly against water. However, the high reactivity of magnesium causes corrosion in its case, despite the protective surface layer.

To increase the resistance, reduce the sensitivity to notching and improve the resistance to corrosion, magnesium can be alloyed mainly with the elements aluminum (AI), zinc (Zn), manganese (Mn), these alloys being present, in general , at room temperature in several phases in the form of mixed crystals and intermetallic phases.

By annealing in solution with subsequent quenching, the toughness or ductility can be influenced and by a slow cooling or quenching by precipitation, the resistance of the material composed of these alloys.

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

However, known magnesium alloys have the disadvantages of a heterogeneous adjustment of microstructure in roughing during continuous extrusion at elevated temperature, as well as a limited ductility of the material at room temperature.

In particular, the low density of the metal represents a substantial advantage of magnesium, such that experts in the field have long faced the desire for magnesium-based modeling alloys.

For example, by a publication "The Effect of Ca Addition on Age Hardening Behaviors and Mechanical Properties in Mg-Zn Alloy" (Materials Science Forum Vol. 419-422 (2003) pages 307-312) it has become known as adding , at an alloy of magnesium and 6% by weight of zinc, from 0.1 to 0.5% by weight of calcium to increase mechanical properties and improve tempering parameters.

With the same approach of objectives of an increase of the resistance and improvement of the resistance to creep was carried out, according to the document "Microstructure and mechanical properties of Mg-Zn-Si-based alloys" (Materials Science and Engineering A357 ( 2003) 314-320) ", an alloy of 1% by weight of Si and, where appropriate, 0.25% by weight of Ca, to a magnesium base material with 6% by weight of Zn.

To create highly resistant and shaped magnesium base alloys, we also tried, as disclosed in the document "Microstructure and Mechanical Properties of Mg-Zn-Ag Alloys" (Materials Science Forum Vol. 419-422 (2003) pages 159) -164) ", to add to an alloy Z6 silver (Ag), being able to obtain with a content of 3% in weight of Ag a remarkable tuning of grain and an increase of the hardness.

Document KR20030055753 discloses a magnesium base alloy containing in percentage by weight: 310% of Zn, 0.5-4.0% of Ag, 0.1-4.0% of Si, 0, 1-2.0% of Ca, magnesium and impurities due to production as rest.

The invention now aims to create a magnesium base alloy that, with a hot pressing of an extrusion slab given the conditioned case, resulting in a rough grinding for fine grain extrusion, the material thereof being highly conformable to higher temperature and at room temperature. In addition, the aim of the invention is to improve or influence the corrosion resistance of the material.

This objective is achieved with a magnesium base alloy composed, in% by weight, of zinc (Zn) more than 0.8, however, less than 6.2

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 Zirconium (Zr)

 traces,

 manganese (Mn)

 more than 0.04;

 calcium (Ca)

 more than 0.04;

 silicon (yes)

 traces,

 antimony (Sb)

 traces,

 aluminum (Al)

 traces,

 silver (Ag)

 more than 0.1,

 magnesium and impurities due to

however, less than 1.0 however, less than 0.6 however, less than 2.0 however, less than 1.0 however, less than 0.5 however, less than 0.5 however , less than 2.0; ion as rest.

The advantages achieved with the magnesium base alloy compound according to the invention lie essentially in a rigorously balanced concentration of elements and a micro-alloy technology in which the interaction of all the elements of the alloy have been taken into account and the reaction kinetics as well as the criteria of grain growth, the advantages in particular being a homogeneous structure of fine grain of the material, a high cold formability and an improvement in its corrosion resistance.

Zinc in contents of more than 0.8 to less than 6.2% by weight in the alloy decisively influences the solidification interval and prevents the formation of very thick columnar crystals during solidification. Concentrations of less than 0.8% by weight of Zn lead to an effect that decreases in an overproportional manner, on the contrary, contents of more than 6.2% by weight give rise to eutectic stiffening of the melt with a disadvantageous effect.

Zirconium acts by precipitation of the melt and with accumulation in the crystallization front with grain refinement. Contents of more than 1.0% by weight of Zr make the precipitations thicker, disadvantageously for the beginning of cracks in the material in case of solicitations.

Manganese in contents of more than 0.04, however, of less than 0.6% by weight has a multiple effect on the alloy. On the one hand, the Mn forges in the melt F, a compound that precipitates, on the other hand, Mn with zirconium forms, at a higher temperature in the melt, phases that can have a grain refining effect.

Calcium with contents of more than 0.04, however, less than 2.0% by weight in the metal results in a formation of phases in the solid alloy, phases that effectively prevent crystal growth as a stabilizer of the Limit of grain. This phase of Ca2Mg6Zn3, which presupposes Zn in the contents mentioned above in the alloy, occurs in the range of 0.1 to 1% by volume of particularly fine form, as well as homogeneously distributed in the material, by which retains an excellent fine grain structure in the material.

The precipitations that stabilize the grain limits in conventional magnesium alloys are generally electrochemical more noble than the magnesium matrix, so that corrosion resistance is damaged by galvanic effects. In the alloy according to the invention, the non-noble phase Ca2Mg6Zn3 precipitates, such that a galvanic corrosion mechanism is significantly reduced. The consequence is an improved resistance to corrosion.

The silicon alloy element in magnesium is only soluble in a very small degree or in traces and forms the Mg2Si phase. Above 1.0% by weight of Si, the phase ratio in the alloy material is large and worsens its mechanical properties.

Antimony must essentially be considered in relation to silicon, because antimony can lead to a modification of the Mg2Si phase, with a required concentration of Sb in the alloy metal having to rise approximately half of that of the Yes.

Although magnesium-based alloys, which can contain aluminum up to 8% by weight and above, also in view of greater material strength and creep resistance, of course they have an application potential, in the material according to the invention aluminum represents an unwanted element. Due to contents of more than 0.5% by weight, fragile grain limit phases of the Mg- ^ AI- ^ type can be produced which also have a corrosion-enhancing effect with a thick configuration. Furthermore, during the extrusion of the material below approximately 230 ° C, fissures are formed that can lead to a brittle pressed piece, and it can also have considerable differences in grain size along the transverse section and the longitudinal direction.

Silver has, as an inhibitor of grain growth, in the alloy according to the invention a high potential in the contents of more than 0.1, however, less than 2.0% by weight. Ag is in these concentrations in the hot state of the alloy material in solution, forming, as it has been found, in case of contents of more than 0.1% by weight of Ag an elevation of the concentration in the grain limits that It is extremely effective against grain growth. In addition, thanks to Ag, a tempering effect of the material can be achieved through the Mg4Ag phase. Ag contents greater than 2.0% in

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Weight have in particular economic disadvantages and in terms of corrosion chemistry.

Preferred chemical compositions of magnesium base alloys according to the invention are indicated in claims 2 and 3.

Particularly important for a homogeneously fine-grained microstructure and high conformability of an object of the alloy according to the invention around room temperature, as found, is the total concentration of the microelements of the Mn alloy , Ca and Si of more than 0.1, however, less than 0.65% by weight in the magnesium base material.

A semi-finished product of a magnesium base alloy according to the invention, which has been formed with a cross-area-to-area ratio of more than 1:16, in particular more than 1:20 of a casting slab to give a Pressed piece at a temperature of approximately 380 ° C, it has a microstructure grain size of less than 10 pm and, in particular, with a substantial isotropic in relation to the cross-section and in the longitudinal direction. The pressed parts according to the invention can be continued forming or pressing at temperatures below 200 ° C, in particular at room temperature, being able to achieve a flawless surface or a glossy surface.

Next, the invention will be supported with some test results.

The chemical composition of the materials examined is indicated in Table 2.

The figures show:

Figure 1, tension-elongation behavior of examined alloys Figure 2, test alloy L1, cast metal structure Figure 3x, test alloy L1, cast metal structure Figure 3.1 magnification scale: 500 pm Figure 3.2 magnification scale: 200 pm Figure 3.3 magnification scale: 50 pm Figure 3.4 magnification scale: 20 pm Figure 4x, test alloy L1, formed

Figure 4.1 transverse metallographic sample edge Figure 4.2 transverse metallographic sample center Figure 4.3 longitudinal metallographic sample edge Figure 4.4 longitudinal metallographic sample center Figure 5, L2 test alloy, cast metal structure Figure 6x, alloy L2 test, cast metal structure Figure 6.1 magnification scale: 500 pm Figure 6.2 magnification scale: 200 pm Figure 6.3 magnification scale: 50 pm Figure 6.4 magnification scale: 20 pm Figure 7x, alloy of L2 test

Figure 7.1 transverse metallographic sample edge Figure 7.2 transverse metallographic sample center Figure 7.3 longitudinal metallographic sample edge Figure 7.4 longitudinal metallographic sample center Figure 8, comparative alloy AZ31, molten metal state Figure 9 comparative alloy ZK31 , molten metal state

Figure 1 shows the result of elongation depending on the tension in the tensile test according to the EN 10002-1: 2001 standard of magnesium base alloys.

Next, reference is made to the alloy denominations and alloy compositions indicated in Table 2.

The sample with a designation L1 of an alloy according to the invention with a conformation by means of an indirect pressing procedure and with a pressing ratio of 1:25, in the tensile test (A50) at room temperature gave an elongation of more of 25% with a maximum tension of approximately 260 MPa.

In the sample of another test alloy L2 according to the invention, after an equal pressing conformation of the ingot at 380 ° C, at room temperature an elongation limit of Rp0.2 = 330 MPa of the material was established, existing as a measure for the ductility an elongation value of more than 15%, in the case of approximately 19%.

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Comparative alloys ZK31, AZ31 and ZM21 presented, as shown in Figure 1, without exception, lower elongation values than materials according to the invention.

In Figure 2, the microstructure of the molten metal of the alloy L1 can be seen. An average grain size of 140 pm was established with an essentially homogeneous structure along the entire cross section of the ingot.

In Figure 3, the largely homogeneous microstructure in the molten metal state of the L1 alloy ingot along the cross-section is shown with different magnifications with a scale indication of 500 pm (Fig. 3.1), 200 pm ( Fig. 3.2), 50 pm (Fig. 3.3) and 20 pm (Fig. 3.4) and shows spherical grains with some phases of grain limit.

Figure 4 shows a material formed with a pressing ratio of 1:25 to 380 ° C of the alloy L1 according to the invention in longitudinal and transverse direction from the marginal and central area of the sample.

Figure 4.1 and Figure 4.2 are images of transverse metallographic sample of the edge and center of the rod, with Figure 4.3 and Figure 4.4 representing the corresponding images of longitudinal metallographic sample. A medium grain size was measured from 9 pm to 6 pm.

In FIG. 5, the microstructure of globatic molten metal of an L2 alloy according to the invention is shown. With a largely homogeneous grain distribution along the ingot, the average grain size amounted to 40 pm.

Figure 6 shows the molten metal microstructure of Figure 5 (L2) in its very fine configuration with scale indications of 500 pm (Fig. 6.1), 200 pm (Fig. 6.2), 50 pm (Fig. 6.3 ) and 20 pm (Fig. 6.4). Reduced fine precipitation phases can be found in the grain boundaries.

Figure 7 shows the microstructure of a pressed part of an alloy L2 of a pressed ingot at a temperature of 380 ° C with a pressing ratio of 1:25 in the transverse direction at the edge (Fig. 7.1) and in the central zone (Fig. 7.2) and in the longitudinal direction at the edge (Fig. 7.3) and in the central zone of the rod (Fig. 7.4.). The average grain size was approximately 2 pm.

The molten metal microstructure of an ingot of a comparative alloy AZ31 is shown in Figure 8. A measurement of the microstructure resulted in a grain size of 360 pm with an essentially homogeneous distribution along the cross-section.

After an extrusion at 380 ° C, the microstructure had partially recrystallized in a thick and heterogeneous manner, so that a safe determination of grain size was not possible.

As depicted in Figure 9, the microstructure of molten metal (colada casting) in the ingot of comparative alloy ZK31 was globulophic and had a grain size of 80 pm with good homogeneity along the cross section.

After hot pressing of the extrusion slab, the extrusion profile had partially recrystallized heterogeneously. A determination of the crystal size with a certain informative capacity in the pressed profile was not possible.

Table 1: Compositions of magnesium alloys according to the state of the art (in% by weight)

 Designation of alloy

 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 Rest

 AZ 91 *

 0.8 0.4 9.0 max. 0.5 Rest

 AM 60 *

   0.25 6.0 Rest

 AZ 31

 1.0 to 1.0 3.0 Rest

* essentially casting alloys

Table. 2: Compositions of materials examined (in% by weight)

 Designation of alloy

 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 Rest

 ZM 21 **

 1.8 0.7 Rest

 ZK 31 **

 2.7 0.5 Rest

 AZ 31

 1.0 0.3 3.0 Rest

no standardized alloy

Claims (3)

 1. Base Alloy

 of compound fine-grained magnesium% by weight of

 zinc (Zn)

 more than 0.8, however, less than 6.2

 Zirconium (Zr)

 traces, however, less than 1.0

 manganese (Mn)

 more than 0.04, however, less than 0.6

 calcium (Ca)

 more than 0.04, however, less than 2.0

 silicon (yes)

 traces, however, less than 1.0

 antimony (Sb)

 traces, however, less than 0.5

 silver (Ag)

 more than 0.1, however, less than 2.0

Magnesium and impurities due to production as rest. 5 2. Magnesium base alloy according to claim 1, wherein the micro-alloy elements Mn, Ca, If they have a total concentration of more than 0.1, however, less than 0.65, preferably more than 0.15, however, less than 0.5. 3. Magnesium base alloy according to claim 1 or 2, wherein the concentration in% by weight of one or more of the alloy elements amounts to

 Zn

 more than 1.0, preferably more than 1.5,

 however, 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

 however, less than 0.4, preferably less than 0.2

 AC

 more than 0.1, preferably more than 0.14

 however, less than 1.0, preferably less than 0.6

 Yes

 less than 0.5, preferably less than 0.2

 Sb

 less than 0.25, preferably less than 0.1

 To the

 less than 0.1, preferably less than 0.08

 Ag

 more than 0.2, preferably more than 0.38

 however, less than 1.2, preferably less than 0.9.

4. Semi-finished product of a magnesium base alloy with a chemical composition according to one of claims 1 to 3, formed with a pressing ratio of at least 1:20, semi-finished product that has a grain size of less than 10 pm and a substantial isotropic. fifteen