AT506283A2 - METHOD AND TOOLS FOR FLOW PRESSING MAGNESIUM KNET ALLOYS - Google Patents

Abstract

In the first stage, a cast bar is extruded to make a blank. The deformation ratio exceeds 1 : 20. For this stage, the microstructure of the material transversely to the direction of deformation, is modified to a grain size less than 20 mu m. One of the elements Zn, Mn , Ca, Si, Sb, Ag is added to the magnesium to manufacture the cast bar and/or up to 2 wt% Zr is added to refine the grain microstructure of the alloy. In the second stage, extrusion billets are produced from the blank; they are taken out at right angles to the direction of extrusion. In the third stage, the billets are extruded transversely to the direction of blank deformation, at room temperature or a temperature no greater than 200[deg] C. No lubricant is used. The shape of the billets is matched with that of the extrusion die, especially at the edges. The equipment used, includes a matrix or die, and a pressing plunger moving relatively to it. The billet alloy has a hexagonal lattice structure. Alternatively, using a temperature below 200[deg] C the wall thickness range is 0.1-13.6 mm, preferably 0,5 mm and less. Independent claims are included for the following: (A) corresponding equipment; (B) and the object produced.

Description

• · · · · ········ Pat. 30 * ·· '· 2 · · - ··· -. ··· ····.

NEUMAN ALUMINUM extrusion press GmbH

Processes and tools for extruding magnesium

Wrought alloys.

The invention relates to methods and tools for extruding magnesium wrought alloys, in which, starting from a cast bolt od. Like. By forming processes, such as extrusion, rolling and / or forging with subsequent heat treatment, a fine-grained structure is generated.

The forming capacity of a material is influenced by many factors: the material properties (crystal lattice, chemical composition, microstructure, anisotropy), the thermodynamic conditions (thermally activated processes, forming speed), the forming behavior (friction, geometry of the forming zone, tool geometry, forming history) and the stress state during forming.

Due to their hexagonal lattice structure, magnesium alloys can only be formed to a limited extent at room temperature. Metals with a hexagonal lattice structure have only one sliding system at room temperature (base plane slip), as well as twinning for deformation, unlike metals with cubic face-centered lattice structure with 5 independent sliding systems. Only at a temperature above 225 ° C are more pyramidal slip planes activated. 1

Pat. 30

Extrusion of magnesium alloys at low temperatures (T <225 ° C) is therefore a major challenge to the material. H.-W. Wagener ["Deep drawing and impact extrusion of magnesium alloys at room temperature", Advanced Engineering Materials 2003, No. 4 and "extrusion of magnesium wrought and cast alloys",

Sheet Metal, Tubes, Profiles, UTF Science 1/2002] attempted to compensate for low forming capacity by increasing the hydrostatic pressure component in extrusion press experiments with magnesium alloys. The compressive stress superposition is achieved by using a closed tool with non-back-turned dies or non-back-turned dies (forward extrusion). During the deformation, one or two force-loaded punches counteract the extrusion direction. ZK60A room-temperature tests using back-pressure full-forward extrusion give no satisfactory result. But an increase in the sample temperature to 250 - 400 ° C leads to error-free workpieces even with non-heated tools. Due to the limited ductility of the investigated alloys (AE42HP, AM20HP, AM70HP, AZ91HP, AZ31B, AZ80, ZK60A), crack-free forward extrusion with backpressure is only possible to a limited extent; full-forward extrusion with backpressure enables flawless workpieces only with increased backpressure or at higher forming temperatures.

Chapman and Wilson ["The room-temperature ductility of fine-grain magnesium", Bull. J. Inst. Met., 1962-63, 91,] showed that in magnesium, by reducing the grain size, the temperature-ductility curve in direction lower temperatures can be shifted, see Fig. 1. This material is uniformly recrystallized magnesium with a grain size of 2 pm. This material is surprisingly ductile at low temperatures and molding rates. 2 • · · · · ··········································

Pat. 30 '·· &quot;

To produce a fine-grained microstructure of Mg alloys, the following methods have been proposed: A. Extrusion or molding with grain refining using special alloying constituents. For example, zirconium has proved to be a very efficient toner for Ai-free Mg alloys. Continuous casting and forming (extrusion, rolling, forging)

The present invention relates to a further development of these technologies, the emphasis being placed on the method steps according to paragraph B, but also the combination of both techniques is used.

The invention is esp. Characterized in that the forming process, a forming or pressing rate of at least 1:20, preferably at least 1:26 is applied and thus grain sizes &lt; 20pm, preferably &lt; 10pm are generated and the extrusion billets taken from the semifinished product produced in the manner described above perpendicular to the forging direction and at temperatures &lt; 200 ° C, preferably extruded at room temperature.

Preferably, by appropriate alloying constituents, such as Zn, Zr, Mn, Ca,

Si, Sb and Ag, a particularly fine-grained structure of the starting material (cast bolts) produced.

Advantageously, during extrusion molding, the extrusion dies are pressed without lubricant coating. In contrast to extruding aluminum, it has been shown that good results can be achieved in the process according to the invention even without lubrication. By eliminating the coating of the slugs with a lubricant results in a significant rationalization of the process.

Pat. 30

In an advantageous development of the invention, the extrusion molding is carried out with tools that are preheated in a conventional manner, at least partially by heating to a temperature of at least 200 ° C.

Further features of the invention will become apparent from the following description of an example and with reference to the drawings. Fig. 1 shows a graph of the dependence of the ductility of temperature and grain size according to Chapman and Wilson. FIGS. 2a to 2d illustrate the change in the casting by extrusion in two different alloys. In the diagram of Fig. 3, the relationship of elongation at break and uniform strain in the tensile test at 120 ° C for different samples is shown. FIG. 4 shows an extrusion tool in axial section; FIG. 5 likewise illustrates an optimized tool version in axial section.

Example 1. Extrusion:

Continuous casting bolts of ZM21 (grain size approx. 1 - 2 mm) and of ZK31 (grain size approx. 80 pm) were extruded with different press ratios (1: 5, 1: 9, 1:14, 1:26). ZM21 and ZK31 extruded profiles with a 1: 9 and 1: 14 press ratio were rolled or forged and heat treated.

The metallographic examination of the extruded starting material showed that the pressing ratios of 1: 5 and 1: 9 are too low to achieve complete kneading.

Extrusion with a compression ratio of 1:26, however, leads to a significant reduction in particle size. The structural formations of the casting condition and of the 4 • ·········

Pat. 30 extruded material (pressing ratio PV = 1:26) are shown in Figs. 2a -2d Fig. 2a shows a micrograph of a cast sample of the alloy ZM21 with a dendritic microstructure with particle sizes of 1-2 mm. By extrusion at a press rate of 1:26, a reduction of the grain sizes to &lt; 200pm achieved (Figure 2b). FIG. 2c illustrates the micrograph of a cast sample of the alloy ZK31, which has an average particle size of 80 μm in its initial state. By extrusion at a press rate of 1:26, the grain size is reduced to &lt; Reduced to 30 pm. (Fig. 2d). 2nd rolls

Pre-heated blanks of ZM21 and ZK31 alloys preheated to 390 ° C were rolled from the as-cast state and extruded at a 1: 9 press ratio to a plate thickness of 22 mm. The slabs were then heat treated at 350 ° C for one hour. The slugs for the extrusion tests were taken from the slabs perpendicular to the rolling direction. 3. Smith forging

With a press ratio of 1: 9 and 1:14 extruded profiles of ZM21 and ZK31 were further formed by forging. The ZM21 profiles were heated to 390 ° C before forging and the ZK31 profiles to 450 ° C. The grain size distribution of the forged ZM21 profiles was very inhomogeneous - areas of 20 μm grains are next to 1 mm grains. For ZK31, the grain size distribution after forging is significantly more homogeneous than for the ZM21. The forged profiles were then heat treated at 375 ° C for one hour.

The slugs for the extrusion direction were taken from the forging samples perpendicular to the forging direction. 5 • · · · ······

Pat. 30 4, tensile tests

To evaluate the compressibility, tensile tests were carried out at 120 ° C with the thermomechanically optimized alloys and the elongation at break and the uniform elongation were determined as relevant guide parameters. To directly compare the results with the characteristics of AA6082 (a typical aluminum alloy for cold extrusion) at room temperature, the characteristics were normalized to AA6082: a characteristic positioned at (1,1) corresponds to the characteristics of AA6082. Values greater than 1 are better and values less than 1 are worse than AA6082. The results of the different thermomechanically treated ZM21 and ZK31 alloys are shown in Fig. 3. Alloy ZK31 can be prepared from cast state by thermo-mechanical methods, e.g. Extrusion and heat treatment or extrusion - forging and heat treatment can be significantly optimized. With the ZM21 alloy, on the other hand, the mechanical characteristics of these processes deteriorate. An optimization is possible here via the way cast - rolls. 5. extrusion

With a hydraulic 100 t press and a 600 t toggle press, cup-shaped parts with a wall thickness of 3.6 mm and a side length of 20 mm were extruded from the optimized ZM21 and ZK31 pre-material in the temperature range 300 - 120 ° C. Up to a temperature of 150 ° C all good parts could be produced, extrusion tests at 100 ° C were successful in any alloy. The metallographic examination of the extruded parts showed that in the critical deformation area at the bottom of the cup at higher temperatures (T> 150 ° C.) and high pressure ratio the flow line course runs almost parallel to the extrusion direction. In extrusion tests at lower temperatures or lower compression ratio of the starting material it comes in this zone to a fault and as a result also to cracking. 6 t Pat. 30 • · · · · · · · · · 6. Extrusion tool.

The extrusion tests with a wall thickness of 1.5 mm and 90 mm side length were carried out on a 6001 toggle press. With the alloy ZK31 could with a tool according to Fig.4. consistently intact parts are pressed. Occasionally small cracks appeared on the rim of the alloy ZM21.

In order to further improve the formability, based on the findings of the first experiments, the geometries of the extrusion tools were modified. Fig. 5 shows such, optimized for the extrusion of magnesium tool.

The next tests were carried out with this optimized tool, with samples with wall thicknesses of 1.5mm, 0.7mm, 0.5mm, 0.35mm and 0.25mm were pressed.

The tool was heated by special heating elements in the die, as well as in the stamp to a temperature of about 200 ° C. In these experiments, the starting material (magnesium) was preheated to a temperature of about 200 ° C. 7. Experimental procedure.

Initially, only the wall thicknesses of 1.5 mm and 0.7 mm intact cups could be produced, whereby it was recognized that the coordination of the geometry of the block to the die has a very significant influence on the stability of the production process.

The parallel computational simulation of the extrusion process for a wall thickness of 0.75 mm shows that in the production of a cup with these dimensions in the region of the bottom very high changes in shape are to be expected. 7 • · • ·

Pat. 30 • ··

After another optimization step, a new series of tests succeeded in producing wall thicknesses of 0.5mm with corresponding quantities. The achieved quality characteristics (wall fluctuation, surface) were at very good values.

Since the process of stable slug preheating at about 200 ° C in mass production poses a technical challenge and would cause additional, considerable production costs, it is an object of the present invention to be able to transform magnesium such as aluminum at room temperature. For this purpose, the Butzenvorwärmtemperatur was continuously reduced in the experiments with 0.5mm wall thickness, until it was possible to press the alloy ZK31 even at room temperature, with preheated tools.

In the last series of experiments, the production of cups with a wall thickness of 0.35 mm was possible for individual parts. This shows that error-free forming is possible at room temperature.

Marktl, on 09th Oct 2006

NEUMAN Aluminum Extrusion Press GmbH 8

Claims (5)

* ········· ··· Pat. in which, starting from a cast bolt od. Like. By forming processes, such as extrusion, rolling and / or forging with subsequent heat treatment, a fine-grained structure is generated, characterized in that the forming process, a forming or pressing rate of at least 1:20, preferably at least 1: 26-applied and thus grain sizes &lt; 20pm, preferably &lt; 10pm produced and the extrusion billets taken from the semifinished product produced in the manner described above perpendicular to the direction of forging and at temperatures &lt; 200 ° C, preferably extruded at room temperature. 2. A method for extruding magnesium wrought alloys according to claim 1, characterized in that, by appropriate alloying components, such as Zn, Zr, Mn, Ca, Si, Sb and Ag, a particularly fine-grained structure of the starting material (cast bolt) is generated. 3. A method for extruding magnesium wrought alloys according to claim 1 or 2 characterized in that the Fließpressbutzen be pressed without lubricant coating. 1 I I Pat. 30 4. A method for extruding magnesium wrought alloys according to one of the claims 1 to 3, characterized in that »the extrusion takes place with tools that are vorgewännt at least partially by heating to a temperature of at least 200 ° C. 5. Tool for extruding magnesium wrought alloys according to the method according to one of the claims 1 to 4, characterized in that the tool has a heating device in a conventional manner, with which it is preheated to a temperature of at least 200 ° C. Marktl, 09. Oct 2006 NEUMAN Aluminum Extrusion Press GmbH