The reason why Samples 1 and 4 obtains better results than Samples 3 and 5 is that forming energy generated at forging was stored as distortion at the inside of the alloy material and the crystal grain was refined by the subsequent heat treatments. Comparing Sample 1 with Sample 4, Sample 1 obtains better results than Sample 4, while both of them have the same forging rate.
The reason for this can be understood as follows: because Sample 4 is lower in forging limit than Sample 1 and is forged to the vicinity of the forging limit, and because Sample 1 includes more strontium than Sample 4 and the strontium exists at high density in the vicinity of grain boundary of the magnesium alloy to reinforce the grain boundary thereby preventing progress of cracks generated along the grain boundary at the tensile test.
Further, Sample 2 obtains better results than Sample 1. It can be understood as the reason that Sample 2 is higher in forging rate than Sample 1.
Next, there will be discussed a relation between strontium content and crystal grain size in a magnesium alloy material. With reference to a melting device 11 shown in FIG. In the surroundings of the crucible 15, heaters 14 are arranged. The crucible 15 is formed by such as mild steel. The temperature of molten metal 16 in the crucible 15 can be measured by a thermocouple Protection gas is supplied, from a gas supplying tube 18, to the surface of the molten metal 16 in the crucible With reference to a casting device 21 shown in FIG.
The die 25 is fixed to a lower end of a plunger 24 of a hydraulic cylinder The air vents 28 are covered by porous metal Ni 27 in order to prevent melted material from blowing off. Under the above construction of the casting device 21, the crucible 15 in which molten metal 16 is entered is placed below the die Then, the plunger 24 is moved downward at a set load and a set velocity.
Thereby, as shown in FIG. As a result, a material cast material 29 as shown in FIG. Each of Samples whose chemical components are shown in the below Table 2 was cast by the use of the above devices 11, Molten alloy was put into a die 25 on condition that a load of the plunger 24 is kN and a moving velocity thereof is 30 mm per second.
Then, a relation between strontium content and crystal grain size in cast materials 29 obtained from the above Samples was examined. Examination results are shown in FIG. In the graph of FIG. In the Figure, respective measuring positions in the vicinity of the surface corresponding to the circular mark and at the inside corresponding to the triangular mark of the cast material 29 are shown.
As understood from the results shown in FIG. In the cast material having strontium of more than 0. Even in the cast material having strontium of lower limit content that is, 0. The casting method using the device of FIG. Accordingly, even if alloy materials having same components are cast by both of the casting methods, obtained cast structures are different from each other. In other words, although the two alloy materials are different in its inside portion from each other, the alloy material obtained by using the device of FIG.
Next, there will be discussed a relation between grain size and plastic formability in a magnesium alloy material. A relation between grain size and plastic formability in a magnesium alloy material was examined. A material to be forged with 28 mm diameter and 42 mm height was cast by the use of a magnesium alloy having chemical components shown in the below Table 3. Then, upsetting as one kind of forging was conducted to the cast material by the method shown in FIG.
Then, as in the test of forging limit shown in Table 1, upsetting formability of the material to be forged was examined, by the use of the above formula 1 , based on a compression allowance till a minute crack generated on the surface of the material to be forged when the material was gradually compressed upset. The results of the test are shown in FIG. From the results of FIG. Next, there will be discussed a relation between strontium content and corrosion resistance in a magnesium light alloy product.
Then, respective forged alloy materials were subjected to above-mentioned heat treatments and formed into board-shaped samples. The board-shaped sample has 50 mm width, 90 mm length and 5 mm thickness. The test results are shown in FIG. From the graph of FIG. First, as shown in FIG. Then, the magnesium alloy material is stirred and mixed, by rotating a stirring bar 34 having a stirring plate 33 as shown in FIGS.
Detailed description is made next about heating and stirring the magnesium alloy material 32 in the crucible 31 at the above first process, with reference to FIG.
Then, the material 32 in the intermediate state is forced into stirring by the stirring plate 33 on the condition shown in Table 5 see FIG. Consequently, as shown in FIG. Then, the sleeve 38 is engaged to an inlet of a die 50 and the alloy material 32 in a semi-solid state is put into the die 50 by actuating the plunger 39, so that the material 32 is cast formed into a blank.
The alloy material 32, which is an intermediate product cast in the above manner, is taken out of the die The alloy material 32 which is an intermediate product cast in the above manner is set, as a material to be forged, on a bottom part 41 of a forging die and forged one time between the bottom part 41 and a top part 40 of the forging die thereby enhancing its mechanical strength.
Next, a cylindrical test piece for compression test with, for example, 15 mm diameter and 30 mm length is formed from the final product obtained by the above processes.
The test piece was subjected to a compression test by the use of a compression test device shown in FIG. Based on data obtained from the results of the above test, there was obtained a relation between solid-phase rate and working limit of the alloy material 32 in a semi-solid state, as shown in FIG.
From FIG. Further, since the magnesium alloy obtained by the semi-solid casting are more excellent in mechanical properties than that obtained by the conventional casting, the subsequently forged magnesium alloy enhances its formability see FIGS. As understood from comparison between FIGS. That is, in addition to enhanced working limit owing to existence of solid phase, excellent forging formability can be achieved because the solid phase is turned into spheres from dendrite.
Further, because of enhanced working limit and excellent forging formability, the alloy material of the present embodiment is sufficiently enhanced in mechanical properties such as tensile strength by one time forging. Furthermore, as understood from FIGS. It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention, and the invention includes all such modifications.
We claim: 1. A method of manufacturing a magnesium light alloy product, comprising the steps of: a preparing a magnesium alloy material by casting a magnesium alloy melted metal into a mold;. The method of manufacturing a magnesium light alloy product of claim 1, wherein the strontium content is not exceeding 0. The method of manufacturing a magnesium light alloy product of claim 2, wherein the forging step b is conducted using a die and a punch.
A magnesium light alloy product comprising strontium, wherein the magnesium light alloy product is made by preparing a magnesium alloy material by casting a melted magnesium alloy metal containing strontium in a range of greater than 0. The magnesium light alloy product of claim 4, wherein the strontium content is not exceeding 0. A method of manufacturing a magnesium light alloy product, comprising the steps of: a preparing a casted magnesium ahoy material from a melted and molded magnesium alloy metal;.
The method of manufacturing a magnesium light alloy product of claim 6, wherein the strontium content is not exceeding 0. The method of manufacturing a magnesium light alloy product of claim 7, wherein the forging step b is conducted using a die and a punch.
There have been commonly known in casting technique that: adding aluminum to magnesium enhances strength of magnesium alloy and presents grain refinement in the cast structure; adding a little amount of manganese to magnesium enhances corrosion resistance and strength due to the grain refinement; and adding a little amount of zinc to magnesium enhances mechanical properties of the magnesium alloy.
For the grain refinement of the cast structure in magnesium alloy, there have been further known techniques of adding a little amount of zirconium and inoculating with carbon, FeCl 3 or the like.
Furthermore, there has been well known a method of producing a metal product in which material is cast in the similar form to a product and then forged refer to Japanese Patent Application Open Gazette No. In case of forging material from ingot to form a product, there have been generally required many forging steps from a rough-forging step to a finish-forging step. In the above method, however, forging steps are reduced because materials are previously cast in the similar form to the product before they are forged.
When casting is combined with forging in the above manner, the forging steps are simplified. However, even if the method is applied to a method of producing a magnesium light alloy product, the forged material cannot obtain satisfactory tensile strength and proof stress because of the limit of forging rate of magnesium alloy material.
The grain refinement of the cast structure is effective on improvement of plastic formability including forgeability and presents enhancements of tensile strength and proof stress. However, conventional measures of adding alloy elements such as Al, Mn and Zn to magnesium have limitations in improvement of the formability due to the grain refinement of the cast structure.
Among various kinds of casting methods, attention has been recently paid to a half-melting casting method in which alloy material is heated and melted in a half-melted state and then formed by solidification. According to this method, cast material having relatively high formability can be obtained. However, in molten alloy merely made in a half-melted state, solid phase part in the molten alloy remains dendrite, thereby reducing fluidity of the cast structure at the formation.
This involves low working limit and insufficient formability. To cope with the above problem, there has been proposed a method of producing a light alloy product, as disclosed in Japanese Patent Publication Gazette No.
However, even by the above method using the magnetical stirring, the dendrite cannot be sufficiently fractured. Thus, working limit is still low and sufficient formability cannot be achieved. Furthermore, when a magnesium light alloy product is used as an application such as an automobile wheel which is exposed to the open air, higher corrosion resistance are required. This invention has its object of providing a light alloy product having excellent plastic formability, high tensile strength, high proof stress and high corrosion resistance.
Further, this invention has another object of providing a method suitable for producing such a light alloy product. Inventors have made efforts in order to overcome the above problems. As a result, they found that: when a set amount of strontium is used as an element for magnesium alloy, the cast structure is refined due to the strontium thereby increasing formability in plastic working; in particular, when strontium is included, at a large amount over a certain extent, in the magnesium alloy, the strontium itself contributes to improvement of the formability because of a different reason from the grain refinement; even when the strontium content of magnesium alloy is relatively small, for example, on condition that a solidification speed cooling speed at the casting is high, the cast structure is gradually refined from the surface towards the inside of casting products in accordance with increase of the strontium content; a magnesium light alloy product enhances its corrosion resistance by including strontium; and when light alloy material is stirred in a half-melted state thereof, dendrite is fractured to turn into spheres.
Based on the foregoing findings, this invention has been realized. Accordingly, a magnesium light alloy product of the present invention has a feature of comprising strontium of 0.
Further, a method suitable for obtaining the magnesium alloy product has a feature of comprising the steps of casting a magnesium alloy material by using molten magnesium alloy containing strontium of 0. According to the method of obtaining the magnesium alloy product by plastically forming the magnesium alloy material cast from the molten magnesium alloy, the strontium contributes to grain refinement of the cast structure and enhances formability in plastic forming. That is, although the grain refinement presents improvement of formability, a grain refinement effect of strontium is saturated when the strontium content of the alloy material reaches to approximately 0.
However, on condition that the solidification speed at the casting is high, the cast structure is further refined according to increase of the strontium content, even if the strontium content is over 0. In this case, particularly, the grain refinement reaches to not only the vicinity of surface of the alloy material but also the inside thereof This will become apparent in the below-mentioned embodiment. In this invention, such a strontium content of the magnesium alloy is set to more than 0.
This presents high tensile strength and high proof stress. In addition, the magnesium alloy product increases its corrosion resistance according to increase of the strontium content This will also become apparent in the below-mentioned embodiment.
As understood from the above, the lowest limit of the strontium content in this invention is set to 0. Further, the reason why the highest limit of the strontium content in this invention is 0. Preferably, the strontium content is set within a range from 0. Setting the strontium content to more than 0.
Although the reason is not obvious, it can be understood that the strontium contributes to enhancement of formability because of not only the grain refinement effect thereof but also another effect due to the use of a large amount thereof. That is, it can be understood that the strontium existing at high density in the vicinity of grain boundary of the magnesium alloy reinforces the grain boundary thereby restraining cracks from generating in the grain boundary at the forming.
The reason why the highest limit of the strontium content is preferably set to 0. At the casting, containing the above strontium into magnesium alloy by means of adding the strontium to molten magnesium alloy is preferable to forming molten alloy by means of melting magnesium alloy material containing the strontium. This enhances the above effects of strontium. Furthermore, it is preferable to apply forging as plastic forming of the magnesium alloy material.
This has the advantage of obtaining grain refinement, high strength and high toughness by executing subsequent heat treatments, i. Accordingly, executing the heating treatments after the forging is a further preferable measure to attain the objects of the present invention. Another method for obtaining a light alloy product according to this invention comprises the steps of: stirring light alloy material in a half-melted state; diecasting the light alloy material in a half-melted state to form a cast material; and then plastically forming the cast material to form a light alloy product.
According to the above method, since light alloy material is stirred in a half-melted state, dendrite of solid phase in molten alloy is fractured to turn into small spheres with grain diameter. Accordingly, a material obtained by casting the molten alloy has a fine structure and a light alloy product obtained by plastically forming the cast material have improved working limit and sufficient formability. In the above method, forging is applicable as plastic forming. By the use of forging, the improved working limit and the sufficient formability can be outstandingly displayed.
Further, a cast material obtained by the half-melting casting method excels one obtained by the conventional casting method in mechanical properties. Accordingly, when the cast material by the half-melting casting method is forged, it performs further excellent mechanical properties by one time forging, in cooperation with enhanced formability.
Consequently, the number of working processes is reduced. Accordingly, a light alloy product, which has been obtained by casting the molten alloy, forging the cast material and conducting the heat treatments to the forged material, has outstandingly improved working limit, sufficient formability, high mechanical strength and high toughness.
Objects, advantages and features of this invention will become more apparent from the following description of embodiment thereof when read in connection with the accompanying drawings. Description is made below about an embodiment of the present invention with reference to the accompanying drawings. First, there will be discussed influences which strontium content of a magnesium light alloy product has on mechanical properties or the like thereof.
As magnesium light alloy products respectively containing set amounts of strontium, Samples 1 to 5 were produced and compared in its mechanical properties or the like with one another. A magnesium alloy material was cast by the use of magnesium alloy A having the following chemical components: 8. As shown in FIG. After the strontium was added, the molten alloy was stirred for ten minutes with keeping the above set temperature, cured for fifteen minutes and then cast.
Then, as shown in FIG. In the Figure, 1 indicates the magnesium alloy material hereafter referred to as Sample 1 , 3 indicates a die, 4 indicates a punch, and 5 indicates a forged material. The formula is:. In the above formula, H and H' indicate respective heights of Sample 1 in a forging direction at times before and after the forging see FIG.
Further, also forging limit was measured. A forging rate at the time when Sample 1 generated a crack 7 was set to the forging limit. Then, heat treatments were conducted to obtained forged material 5.
Then, obtained forged material was subjected to the same heat treatments as in Sample 1. Yakovenko E. Aleksenko I. This process is experimental and the keywords may be updated as the learning algorithm improves. This is a preview of subscription content, log in to check access. Google Scholar.
Abushenkav, V. Chernetsky, V. Laboratiria , London Venkateswara Rao, Weifang Yu and R. A 20A Fridlander, Yu. Dolzhasky, V. Sandler, V.
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