Patent Application
20240110265
The present application claims priority of Korean Patent Application No. 10-2022-0126371 filed on Oct. 4, 2022, the entire contents of which is incorporated herein for all purposes by this reference.
The present disclosure relates to a sintered material for aluminum die casting and a method for manufacturing the same, and more particularly, to a sintered material for aluminum die casting, which can prevent the strength from being lowered even after steam treatment, and a method for manufacturing the same.
Recently, in order to improve the fuel economy of a vehicle, weight reduction of vehicle parts is in progress.
For example, there is a trend to replace engine parts of internal combustion engines, which have been usually made of cast iron, with those made of aluminum. However, when the parts made of aluminum alone are used, although weight reduction can be achieved, there is a disadvantage in that the rigidity required for the parts is not satisfied.
Therefore, an insert is manufactured from cast iron to form a region requiring characteristic properties, the insert is mounted inside the mold, and molten aluminum is injected into the mold at high pressure to produce a cast product.
For example, as to a bed plate constituting an internal combustion engine, the main stress part employs a cast iron insert while the bed plate body is manufactured by aluminum die casting.
However, the insert made of cast iron and the bed plate body made of aluminum have a problem of low bonding strength as they are different types of metal.
Therefore, in order to increase the bonding force between the insert and the bed plate body, a process of forming a thermal spraying coating layer by aluminum thermal spraying on the surface of the insert is added.
However, this method has a problem in that the manufacturing cost increases due to the increase in the number of processes.
Therefore, recently, a technique for omitting the thermal spraying treatment process by manufacturing an insert by a sintering method has been studied and used.
However, when a sintered material is applied to an insert, there may occur a problematic situation in which residues such as lubricants remaining in the pores of the sintered material are vaporized during preheating and die casting of the insert and smoke is generated during preheating, or air bubbles are transferred into the molten metal when being in contact with the molten metal. In order to solve this problem, the insert is sintered and then subjected to the steam treatment.
Meanwhile, a representative material applied to the sintered material is a Fe—Cu—C-based powder. And, according to the use of the sintered parts, the steam treatment is performed to secure abrasion or airtightness.
However, when the sintered material is steam-treated and then used as an insert for aluminum die casting, there is a problem in that the fatigue strength of the part is significantly reduced.
It is confirmed that the reason that the fatigue strength of the sintered material is because in the case of steam treatment of sintered material, the treatment is carried out in the temperature range of 400 to 600° C., and Cu solidificated in the Fe matrix during the sintering process of 1100 to 1150° C. is crystallized on the surface portion of the powder, and weakens the surface portion of the powder.
In order to avoid this problem, the technology of performing sol-gel treatment at a temperature near 200° C. rather than the temperature range of 400 to 600° C. was introduced to the steam treatment. In this case, Cu elements are finely precipitated, but the formation of Fe3O4 is weak.
The matters described above as the background art are only for facilitating a better understanding of the background of the present disclosure, and should not be taken as an acknowledgment that they correspond to the prior art already known to those of ordinary skill in the art.
The present disclosure provides a sintered material for aluminum die casting which does not contain copper (Cu), and can prevent the strength from being lowered even after the steam treatment, and a method for manufacturing the same.
Technical objects, which the present disclosure is to accomplish, are not limited to the aforementioned ones, and other technical objects not mentioned above may be clearly appreciated from the description of the present disclosure by a person having ordinary skill in the art to which the present disclosure belongs.
The sintered material for aluminum die casting according to an embodiment of the present disclosure is a sintered material used as an insert at the time of aluminum die casting, and contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, and C: 0.64 to 0.87 wt %, with the remainder being Fe and other unavoidable impurities.
The sintered material further includes one or two or more kinds selected from the group consisting of Mn, Ni and S, and a total content of Mn, Ni and S is in a range of 0.15 to 0.45 wt %.
The sintered material does not contain Cu.
The sintered material has a yield strength of 400 MPa or more, and a fatigue strength of 150 MPa or more.
The sintered material has a density of 6.8 to 7.2 g/cm3.
On a surface of the sintered material, a surface protective layer made of iron oxide is formed.
Cu is not crystallized on the surface protective layer.
Meanwhile, a method of manufacturing a sintered material for aluminum die casting according to an embodiment of the present disclosure includes preparing an iron-based pre-alloy powder containing chromium (Cr) and molybdenum (Mo), preparing an iron-based pre-alloy mixture by mixing carbon powder, a functional additive, and a lubricant with the iron-based pre-alloy powder, preparing a molded material by molding the iron-based pre-alloy mixture, preparing a sintered material by sintering the molded material, and steam-treating the sintered material.
In the preparing of the iron-based pre-alloy powder, the iron-based pre-alloy powder preferably contains Cr: 0.72 to 0.98 wt %, and Mo: 0.10 to 0.20 wt %, with the remainder being Fe and other unavoidable impurities.
In the preparing of the iron-based pre-alloy powder, the iron-based pre-alloy powder further includes one or two or more kinds selected from the group consisting of Mn, Ni and S, and a total content of Mn, Ni and S is in a range of 0.15 to 0.45 wt %.
In the preparing of the iron-based pre-alloy powder, the iron-based pre-alloy powder does not contain Cu.
In the preparing of the iron-based pre-alloy mixture, the iron-based pre-alloy mixture is prepared by mixing a functional additive and a lubricant with the iron-based pre-alloy powder, so that the iron-based pre-alloy mixture contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, C: 0.63 to 0.87 wt %, functional additive: 0.10 to 0.20 wt %, and lubricant: 0.54 to 0.66 wt %, with the remainder being Fe and other unavoidable impurities.
In the preparing of the sintered material, the sintered material contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, C: 0.64 to 0.87 wt %, and functional additive: 0.10 to 0.20 wt %, with the remainder being Fe and other unavoidable impurities.
The preparing of the sintered material is sintering the molded material at a temperature of 1100 to 1150° C. for 20 to 60 minutes in a nitrogen and hydrogen mixed gas atmosphere, and then air-cooling the molded material.
The steam-treating of the sintered material is treating the sintered material in a steam atmosphere at a temperature of 400 to 600° C. for 30 to 60 minutes.
In the steam-treating of the sintered material, a surface protective layer made of iron oxide is formed on a surface of the sintered material.
In the steam-treating of the sintered material, Cu is not crystallized on the surface protective layer.
After the steam-treating of the sintered material, the microstructure of the sintered material is pearlite.
According to an embodiment of the present disclosure, as the alloy components distributed in the iron powder are prevented from precipitating on the surface of the powder after performing aluminum die casting by the use of the sintered material as an insert and the steam treatment of the sintered material through the adjustment of the composition of the sintered material, the alloy component distributed in the iron powder is prevented from precipitating to the surface of the powder, the effect of preventing the fatigue strength of the parts to which the sintered material is applied from being lowered can be expected.
In particular, the Cu-free sintered material according to the embodiment of the present disclosure can be expected to have the effect of maintaining excellent fatigue strength of parts compared to the Cu-containing sintered material.
Hereinafter, exemplary embodiments disclosed herein will be described with reference to the accompanying drawings, in which identical or like components are given like reference numerals regardless of drawing numbers, and description thereof will not be repeated.
Suffixes for components, “module”, “unit” and “part” used in the following description, will be given or used in place of each other taking only easiness of specification preparation into consideration, and they do not have distinguishable meanings or roles by themselves.
In describing the embodiments disclosed herein, it is noted that the detailed description for related known arts may be omitted herein so as not to obscure essential points of the disclosure. Further, the accompanying drawings are intended to facilitate a better understanding of examples disclosed herein, and the technical spirit disclosed herein is not limited by the accompanying drawings, and rather should be construed as including all the modifications, equivalents and substitutes within the technical idea and technical scope of the disclosure.
The terms including ordinal number such as, first, second and the like may be used to explain various components, but the components should not be limited by these terms. Said terms are used in order only to distinguish one component from another component.
Further, when one component is referred to as being “connected” or “accessed” to another element, it should be understood that the one component may be directly connected or accessed to the other component or any intervening component may also be present therebetween. Contrarily, when one component is referred to as being “directly connected” or “directly accessed” to another component, it should be understood as that no other element is present therebetween.
Singular expressions may include the meaning of plural expressions unless the context clearly indicates otherwise.
Terms such as “include (or comprise)”, “have (or be prepared with)”, and the like are intended to indicate that features, numbers, steps, operations, components, parts, or combinations thereof written in the following description exist, and thus should not be understood as that the possibility of existence or addition of one or more different features, numbers, steps, operations, components, parts, or combinations thereof is excluded in advance.
The sintered material for aluminum die casting according to an embodiment of the present disclosure is a material used as an insert during aluminum die casting, and may be applied to engine parts of an internal combustion engine that must maintain excellent fatigue strength while achieving weight reduction. For example, a cylinder block, a piston pin, a bed plate, and the like constituting an engine of an internal combustion engine may be manufactured by aluminum die casting using the sintered material according to the present disclosure.
Such sintered material may be manufactured by mixing the iron-based pre-alloy powder with a carbon powder, a functional additive, and a lubricant. However, the lubricant is vaporized during the process of sintering the sintered material, so that it does not remain in the final sintered material.
Therefore, the sintered material for aluminum die casting according to an embodiment of the present disclosure contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, and C: 0.64 to 0.87 wt %, with the remainder being Fe and other unavoidable impurities.
Additionally, the sintered material may further contain one or two or more kinds selected from the group consisting of Mn, Ni and S in order to secure physical properties. In this case, the total content of Mn, Ni and S is preferably in a range of 0.15 to 0.45 wt %.
In addition, the sintered material may contain the functional additive at a level of 0.10 to 0.20 wt %. In this case, various functional additives may be applied as the functional additive to secure physical properties, formability, and processability of the sintered material.
Meanwhile, Cr and Mo, which are the main alloy elements of the pre-alloy iron-based powder forming the sintered material, are components contained to secure rigidity in structural parts, and are alloy elements that stabilize pearlite which is the microstructure of the pre-alloy iron-based powder.
So, when Cr and Mo are contained less than the presented content range, the pearlite, which is a microstructure, is not stably formed, and, when they are contained more than the presented content range, the effect of improving the physical properties is inadequate, and there is a problem in that the formability is lowered or the production cost of the sintered material is increased.
Additionally, C is a material manufactured in the form of carbon powder separately from the pre-alloy iron-based powder and mixed with the pre-alloy iron-based powder, and is an additive element that stabilizes the pearlite along with Cr and Mo.
So, when C is contained less than the presented content range, the pearlite, which is a microstructure, is not stably formed, and when it is contained more than the presented content range, there is a problem in that the formability is lowered.
Meanwhile, the sintered material according to the present embodiment preferably does not contain Cu. Therefore, when an insert for aluminum die casting is manufactured using the sintered material, and when the insert is steam-treated for aluminum die casting, it is possible to fundamentally prevent the crystallization of Cu in a temperature range during the steam treatment. In addition, it is possible to fundamentally prevent Cu from being precipitated in the heating temperature section during the preheating of the insert.
And, on the surface of the sintered material according to the present embodiment, a surface protective layer made of iron oxide such as Fe3O4 is formed by the steam treatment. Therefore, it is possible to solve the problem that the residues in the pores inside the sintered material are vaporized or air bubbles are transferred to the inside of the molten metal during the preheating and die casting process for aluminum die casting using the sintered material.
In addition, it is characterized that Cu is not crystallized on the surface protective layer.
By adjusting the components of the sintered material as described above, the sintered material can maintain a yield strength of 400 MPa or more and a fatigue strength of 150 MPa or more.
And, the sintered material preferably has a density of 6.8 to 7.2 g/cm3.
A method for manufacturing the sintered material as described above will be described.
A method of manufacturing a sintered material for aluminum die casting according to an embodiment of the present disclosure includes preparing an iron-based pre-alloy powder containing chromium (Cr) and molybdenum (Mo), preparing an iron-based pre-alloy mixture by mixing carbon powder, a functional additive, and a lubricant with the iron-based pre-alloy powder, preparing a molded material by molding the iron-based pre-alloy mixture, preparing a sintered material by sintering the molded material, and steam-treating the sintered material.
The preparing of the iron-based pre-alloy powder is a step of preparing the iron-based pre-alloy powder constituting the sintered material.
In this case, the iron-based pre-alloy powder preferably contains Cr: 0.72 to 0.98 wt %, and Mo: 0.10 to 0.20 wt %, with the remainder being Fe and other unavoidable impurities.
And, the iron-based pre-alloy powder may further include one or two or more kinds selected from the group consisting of Mn, Ni, and S. In this case, the total content of Mn, Ni and S is preferably kept in a range of 0.15 to 0.45 wt %.
In particular, the iron-based pre-alloy powder preferably does not contain Cu in order to fundamentally prevent the problems caused by the inclusion of Cu.
The preparing of the iron-based pre-alloy mixture is a step of mixing the carbon powder, the functional additive and the lubricant with the iron-based pre-alloy to form the sintered material.
In this case, the iron-based pre-alloy mixture is obtained by measuring the contents of the carbon powder, the functional additive and the lubricant and mixing them with the iron-based pre-alloy powder, so that the iron-based pre-alloy mixture contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, C: 0.63 to 0.87 wt %, functional additive: 0.10 to 0.20 wt %, and lubricant: 0.54 to 0.66 wt %, with the remainder being Fe and other unavoidable impurities.
The preparing of the molded material is a step of molding the iron-based pre-alloy mixture into a predetermined shape. For example, the iron-based pre-alloy mixture is press-molded to manufacture an insert of a desired shape.
The preparing of the sintered material is a step of sintering the molded product formed into a predetermined shape.
The atmosphere for sintering the molded material is carried out in a mixed gas atmosphere of nitrogen and hydrogen. At this time, the mixing ratio of nitrogen and hydrogen is preferably maintained in the range of 90%±10%: 10%±10%.
In addition, the molded material is preferably maintained at a temperature of 1100 to 1150° C. for 20 to 60 minutes, and then cooled in air cooling conditions.
The steam-treating of the sintered material includes forming a surface protective layer made of iron oxide on the surface of the sintered material by steam-treating the sintered material on which the sintering and the cooling have been completed.
At this time, the steam treatment is preferably performed by treating the sintered material in a steam atmosphere at a temperature of 400 to 600° C. for 30 to 60 minutes.
In the sintered material that has been steam-treated in this way, Cu is not crystallized on the surface protective layer, and the surface protective layer is made of iron oxide such as Fe3O4.
And, the microstructure of the sintered material is formed in pearlite.
Next, the present disclosure will be described through Comparative Examples, and Examples.
First, the existing materials applied to Comparative Examples, and Examples used an iron-based pre-alloy mixture whose composition was adjusted to Fe-3Cu-0.7C by mixing Cu powder and C powder with iron-based powder, and the inventive material used an iron-based pre-alloy mixture whose composition was adjusted to Fe-0.85Cr-0.15Mo-0.75C by mixing iron-based pre-alloy powder containing Cr and Mo with C powder. At this time, the existing material and the inventive material were each mixed with 0.15 wt % of a functional additive and 0.6 wt % of a lubricant.
And, after preparing the sintered materials while changing the density according to the adjustment of the pressing force of the molding, the presence or absence of steam treatment, and the type of atmospheric gas of the sintering as shown in Table 1 below, density, Young's modulus, yield strength, tensile strength and fatigue strength of the respective sintered materials were measured, and the results are shown together in Table 1.
As can be seen from Table 1, it was confirmed that the Young's modulus proportionally changed according to the change in density in Comparative Examples and Examples.
Meanwhile, in the case of Comparative Example 1 which used an existing material containing Cu, but was not subjected to the steam treatment, and employed ENDO as the sintering gas, it was confirmed that the yield strength and the tensile strength were excellent, and that the fatigue strength was not lowered.
However, in the case of Comparative Example 2 which used an existing material containing Cu, but was subjected to the steam treatment, and employed ENDO as the sintering gas, it was confirmed that the yield strength and the tensile strength were excellent, but that the fatigue strength was significantly lowered.
And, in the case of Comparative Example 3 which used an inventive material not containing Cu, and was subjected to the steam treatment, and employed ENDO as the sintering gas, it could be confirmed that the yield strength and the tensile strength were lowered, and particularly that the fatigue strength was significantly lowered.
Additionally, in the case of Comparative Example 4 which used an inventive material not containing Cu, but was not subjected to the steam treatment, and employed a mixed gas of nitrogen and hydrogen as the sintering gas, it was confirmed that the tensile strength and fatigue strength were excellent, but that the yield strength was lowered.
Meanwhile, in the case of Examples 1 and 2 which used a mixed gas of nitrogen and hydrogen as a sintering gas and was subjected to the steam treatment while using an inventive material that does not contain Cu, it was confirmed that the yield strength, the tensile strength and the fatigue strength were all excellent. In particular, it was confirmed that Examples 1 and 2 both had a yield strength of 400 MPa or more, and a fatigue strength of 150 MPa or more.
Next, the fracture surfaces of the sintered materials manufactured according to the component change of the sintered material were compared.
First, after measuring the fatigue strengths of the sintered materials manufactured according to Comparative Example 2 and Example 1, the fracture surfaces were observed, and the fracture surface component of Comparative Example 2 was analyzed.
Comparing
In addition, as can be seen in
Next, in order to find out the microstructures of the sintered materials according to Comparative Examples and Examples, the microstructures of Comparative Example 2 and Example 1 were observed, and the results are shown in
As can be seen from
Next, the change in strength according to the component change of the iron-based pre-alloy mixture was investigated.
At this time, the inventive material basically employed an iron-based pre-alloy mixture whose composition was adjusted to Fe-0.85Cr-0.15Mo-0.75C by mixing an iron-based pre-alloy powder containing Cr and Mo with a C powder, and Examples were prepared, in which the contents of C, Cr and Mo had been varied. At this time, the existing material and the inventive material were each mixed with 0.15 wt % of a functional additive and 0.6 wt % of a lubricant.
And, the sintered materials were prepared while changing the density according to the adjustment of the pressing force during the molding as shown in Table 2 below, and then the yield strength and tensile strength thereof were measured, and the results are shown together in Table 2.
As can be seen in Table 2, it could be confirmed that all of Examples 3 to 6 in which the density was maintained and the contents were changed within the ranges of the components and contents presented in the present disclosure maintained excellent yield strength and tensile strength. In particular, it was confirmed that all of Examples 3 to 6 maintained a yield strength of 400 MPa or more.
Although the present disclosure has been described with reference to the accompanying drawings and the above-described preferred embodiments, the present disclosure is not limited thereto, but limited by the following claims. Accordingly, those of ordinary skill in the art can variously change and modify the present disclosure within a scope which does not depart from the technical idea of the claims to be described later.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0126371 | Oct 2022 | KR | national |
