KR20210012427A - Heat treatment method for dissimilar material gap minimizes of die-casting products - Google Patents

Abstract

According to one aspect of the present invention, provided is a thermal treatment method for minimizing a dissimilar material gap between diecasting materials. The thermal treatment method for minimizing a dissimilar material gap between diecasting materials includes: a first thermal treatment step of creating a compound containing oxygen in at least one part of the surface of a first member by heating the first member manufactured of cast iron before being inserted into a mold; and a step of inserting the first member into the mold and then performing aluminum diecasting, thereby forming a second member fixing the first member and coming in contact with at least one part of the first member. A separation distance between interfaces of the first and second members can be 10μm to 35μm.

Description

Heat treatment method for dissimilar material gap minimizes of die-casting products}

The present invention relates to a heat treatment method for minimizing the heterogeneous gap of a die-casting material, and more particularly, to a heat treatment method for minimizing the heterogeneous gap of a die-casting material applied to an automobile engine.

Die casting is a very important base technology in the automobile industry. It is a method of manufacturing products by filling a metal such as molten aluminum or magnesium in a precisely manufactured mold at high speed and high pressure. It is widely used in manufacturing parts.

Among automobile engine parts, the low crankcase (or bed plate), which is bolted to the skirt part of the engine block, generates vibration (explosion load) from the bearing cap as the crankshaft rotates when the engine is driven. The body support and a bearing insert installed at an intermediate portion of the main body support, that is, a journal portion that directly distributes the explosion load of the engine, are included.

The low crank case as described above was mainly applied with a single material made of cast iron, but in recent years, in order to optimize the front and rear weight ratio of the vehicle, and to respond to the demand for weight reduction and high output, the main body was manufactured by the aluminum die casting method, The bearing insert was made of cast iron with high rigidity.

However, in the conventional low crankcase as described above, the bearing insert is manufactured by sand casting, so that the production volume is low, and because dissimilar metals are inserted into the aluminum forming the main body support, due to the difference in thermal expansion characteristics, it is compared with the low crankcase body. The bonding property is deteriorated, and due to this, a gap is generated in the bonding surface, resulting in a problem that the load is not smoothly distributed.

In addition, the conventional low crankcase has to process cast iron and aluminum at the same time, but it is made of heterojunction, so productivity is lowered due to post-processing according to different cutting conditions, and it is difficult to manage the processing roughness, thereby increasing the manufacturing cost, as well as reducing defective products. When it occurs, there is a problem that reproduction is virtually impossible.

Recently, in order to solve the problem of the low crank case made of cast iron and aluminum as described above, a method of manufacturing a bearing insert by hot forging method using a high-strength aluminum alloy has been developed, but the aluminum hot forging method has There is a disadvantage in that the manufacturing process is complicated and the manufacturing cost increases due to diversity and excessive process steps.In addition, since hot forging products are made through a number of forging and trimming operations, not only the working time and the working process are lengthened, but also excessive There were various problems, such as manufacturing cost incurred and overall productivity was lowered.

Accordingly, the present invention is to solve various problems including the above problems, and provides a heat treatment method for minimizing heterogeneous gaps in die-casting materials that can improve adhesion by minimizing the gap in the joint surface with the low crankcase body. It aims to do. However, these problems are exemplary, and the scope of the present invention is not limited thereby.

According to an aspect of the present invention for solving the above problem, a heat treatment method for minimizing the gap between different kinds of die casting materials is provided.

The heat treatment method for minimizing the heterogeneous gap of the die-casting material includes: a first heat treatment step of heating a first member made of cast iron before inserting it into a mold to generate a compound containing oxygen on at least a portion of the surface of the first member; And forming a second member that contacts at least a portion of the first member and fixes the first member by performing aluminum die casting after inserting the first member into the mold. Including, the first A separation distance between the member and the interface of the second member may be 10 μm to 35 μm.

In the heat treatment method for minimizing the heterogeneous gap of the die-casting material, the first heat treatment may be performed in a temperature range of 200°C to 800°C.

In the heat treatment method for minimizing the heterogeneous gap of the die-casting material, the first heat treatment may heat the first member to the temperature range and then cool to room temperature.

In the heat treatment method for minimizing the heterogeneous gap of the die casting material, the first heat treatment may be performed for 0.5 to 1.5 hours.

In the heat treatment method for minimizing the heterogeneous gap of the die-casting material, after the first heat treatment step, a second heat treatment step of reheating the first member may be performed.

In the heat treatment method for minimizing the heterogeneous gap of the die-casting material, the second heat treatment may be performed in a temperature range of 100°C to 250°C.

In the heat treatment method for minimizing the heterogeneous gap of the die-casting material, the second heat treatment may be performed for 0.5 to 1.5 hours.

According to an embodiment of the present invention made as described above, it is possible to provide a heat treatment method for minimizing heterogeneous gaps in die-casting materials that can improve bonding by minimizing gaps on the bonding surface with the low crankcase body through optimization of the heat treatment process I can. Of course, the scope of the present invention is not limited by these effects.

1 is a process flow diagram schematically illustrating a heat treatment method for minimizing heterogeneous gaps in a die-casting material according to an embodiment of the present invention.
2 is a photograph of a sample manufactured by a heat treatment method for minimizing heterogeneous gaps in a die casting material according to an experimental example of the present invention.
3 and 4 are photographs of an analysis of a bonding surface of samples prepared by a heat treatment method for minimizing heterogeneous gaps in a die-casting material according to an experimental example of the present invention with a scanning electron microscope.
5 is a result of line scan analysis of components near the bonding surface of samples manufactured by a heat treatment method for minimizing heterogeneous gaps in a die-casting material according to an experimental example of the present invention.
6 is a result of point analysis of components according to positions in the region shown in FIG. 5.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, and the scope of the present invention is as follows. It is not limited to the examples. Rather, these embodiments are provided to make the present disclosure more faithful and complete, and to completely convey the spirit of the present invention to those skilled in the art.

According to one aspect of the present invention, it provides a heat treatment method for minimizing the gap between the die-casting material. Here, the heterogeneous gap means a gap formed in the joint surface between the aluminum low crankcase body and the cast iron bearing cap.

Weight reduction must be accompanied by regulations on automobile fuel economy and carbon dioxide (CO2) emissions. Conventionally, the bad plate of an automobile is made of cast iron and satisfies all of abrasion resistance, strength, and hardness, so it is suitable for friction parts. However, since the weight was 10.5 kg, aluminum was applied to the bed plate to reduce the weight by half. However, it was not suitable for use as a friction part due to lack of abrasion resistance, strength and hardness.

To solve this, cast iron was used as the bearing cap, but aluminum was substituted for the bed plate, and a cast iron material was applied to the area requiring abrasion resistance, while controlling the weight of 6.5 kg while maintaining abrasion resistance, strength and hardness similar to those of the prior art. . However, since it is a heterogeneous material, a gap is generated in the bonding surface due to the difference in the coefficient of thermal expansion. In the present invention, to solve this problem, the gap is minimized by pre-heating the bearing cap.

1 is a process flow diagram schematically illustrating a heat treatment method for minimizing heterogeneous gaps in a die-casting material according to an embodiment of the present invention.

Referring to FIG. 1, the heat treatment method for minimizing the heterogeneous gap of the die-casting material according to an embodiment of the present invention is a first heat treatment of heating a first member to generate a compound containing oxygen on at least a part of the surface of the first member. Step (S100), a second heat treatment step (S200) of reheating the first member, and a step of forming a second member fixing the first member by performing aluminum die casting after inserting the first member into the mold (S300) It may include.

The first heat treatment step S100 of heating the first member may be performed for 0.5 to 1.5 hours at a temperature range of 200°C to 800°C. Here, the first member is made of cast iron and is cooled to room temperature after heating to a predetermined temperature before being inserted into a mold. By performing the first heat treatment in the temperature range, the surface of the first member is oxidized. A compound containing oxygen is produced on the surface of the first member by the oxidation reaction.

Thereafter, a second heat treatment step S200 of selectively reheating the first member may be performed. The second heat treatment step (S200) may be performed for 0.5 to 1.5 hours at a temperature range of 100°C to 250°C. In the second heat treatment step S200, the stress generated in the process of cooling after heating to a predetermined temperature range in the first heat treatment step S100 is removed.

In the step of forming a second member for fixing the first member by performing aluminum die casting after inserting the first member into the mold (S300), the first member made of cast iron is inserted into the mold and then aluminum die casting is performed, A second member that contacts at least a portion of the first member and fixes the first member may be formed.

In order to perform die casting, it must be cooled to room temperature after performing the first heat treatment before inserting the first member into the mold. If the second heat treatment is continuously performed after the first heat treatment, the first member must be inserted into the mold after cooling to room temperature after the second heat treatment.

A separation distance between the interface between the first member and the second member may be 10 μm to 35 μm. Conventionally, the gap between the interfaces was 40 μm or more, and the gap was wide open. However, by oxidizing the surface of the cast iron material through the first heat treatment, the heterogeneous gap could be reduced. This is a very important factor.By selectively oxidizing the surface of the cast iron material and reacting with aluminum during die casting, a compound containing oxygen is generated at the interface between the first member and the second member, thereby reducing the gap. And improves interfacial bonding. Through the second heat treatment, the diffusion of atoms is induced to form an intermetallic compound, and the heterogeneous gap is reduced.

Meanwhile, the second heat treatment step S200 may be omitted depending on the heating temperature range and cooling rate of the first heat treatment step S100. For example, as shown in FIG. 1, die casting may be performed after sequentially performing a first heat treatment and a second heat treatment, or die casting may be performed immediately after the first heat treatment.

Hereinafter, embodiments for aiding understanding of the present invention will be described. However, the following experimental examples are only to aid understanding of the present invention, and the present invention is not limited to the following examples.

<Example>

A bad plate sample to which different materials were applied was prepared by using the heat treatment method for minimizing the gap between the die-casting materials according to the embodiment of the present invention. Example 1 by performing the first heat treatment for 1 hour at a temperature of 200°C and 800°C for 1 hour before inserting the bearing cap made of cast iron (FCO 500) into the mold, and then performing aluminum (ADC 12) die casting after inserting into the mold. Samples and Example 2 samples were prepared respectively.

The same bearing cap was subjected to the first heat treatment for 1 hour at a temperature of 800°C, followed by the second heat treatment at 100°C, 150°C, 200°C and 250°C for 1 hour, and then inserted into the mold and aluminum die casting. Thus, Example 3 samples to Example 6 samples were prepared respectively.

Meanwhile, in order to compare this, a sample of Comparative Example 1 was prepared by performing die casting without performing heat treatment on the same bearing cap.

Each experimental condition is summarized in Table 1 below.

division 1st heat treatment 2nd heat treatment Temperature(℃) Time(Hr) Temperature(℃) Time(Hr) Comparative Example 1 0 0 0 0 Example 1 200 One 0 0 Example 2 800 One 0 0 Example 3 800 One 100 One Example 4 800 One 150 One Example 5 800 One 200 One Example 6 800 One 250 One

2 is a photograph of a sample manufactured by a heat treatment method for minimizing heterogeneous gaps in a die-casting material according to an experimental example of the present invention, and FIGS. 3 and 4 are a heat treatment method for minimizing heterogeneous gaps in a die-casting material according to the experimental example of the present invention. This is a photograph of the bonding surfaces of the prepared samples analyzed with a scanning electron microscope.

Figure 2 (a) is a photograph of a sample of Example 1 manufactured by a heat treatment method for minimizing heterogeneous gaps in a die-casting material according to an embodiment of the present invention, in which a cast iron bearing cap is located in a red circle marked by a dashed line, and aluminum die casting It was confirmed that it was fixed. In (b) of FIG. 2, numbers are designated for each position of the bearing cap, and measurement positions are described in FIGS. 3 and 4. For example, when the gap was measured at the first position of the sample in Comparative Example 1, Comparative Example 1 (1), and when the gap was measured at the third position, it was expressed as Comparative Example 1 (3).

3 and 4 show an average by analyzing the bonding surfaces of the samples with a scanning electron microscope, and measuring the gap several times for each sample.

Referring to FIGS. 3 and 4, in the case of the example samples manufactured using the heat treatment method for minimizing the heterogeneous gap of the die-casting material according to the present invention, the heterogeneous gap in the sample of Example 2 had the smallest value of 14.77 μm, and It was measured to have the largest value of 33.38 μm in the sample of Example 1. It was confirmed that the value of the heterogeneous gap was improved in all of the example samples compared to the comparative example 1. In addition, in the case of the samples of Example 1 and Example 2, it was confirmed that the heterogeneous gap was improved even when the second heat treatment was not performed. This means that the second heat treatment can be optionally omitted depending on the conditions of the process.

5 is a line scan analysis result of components near the bonding surface of samples manufactured by a heat treatment method for minimizing heterogeneous gaps in a die-casting material according to an experimental example of the present invention, and FIG. 6 is an area shown in FIG. This is the result of point analysis of the component according to the location in.

5 is a result of line scan analysis in the direction of the arrow, in the case of Example 4 sample prepared using the heat treatment method for minimizing the heterogeneous gap of the die-casting material according to the present invention, iron (Fe ) It was confirmed that a large amount of the compound containing the component was contained, and the spacing around the intersection of the compound containing the iron component with the compound containing the aluminum (Al) component was relatively narrow.

6 is a result of randomly selecting and analyzing 3 points for each location in the same area as the area shown in FIG. 5, and then performing an average. In the case of the Example 4 sample, 25.8 wt% of oxygen (O ) It could be confirmed that the component was detected. On the other hand, in the case of the sample of Comparative Example 1, no oxygen component was detected in any region including the bonding interface. The oxygen component was generated by the first heat treatment, and it was confirmed that a compound containing oxygen was formed on the surface of the cast iron bearing cap.

In addition, it was confirmed that the AlFeSi-based compound was formed at the bonding interface. Therefore, a compound containing oxygen is generated at the interface between the cast iron bearing cap and the aluminum die-casting material by the first heat treatment according to the present invention, and then AlFeSi-based compounds are generated at the interface between the cast iron bearing cap and the aluminum die-casting material by the second heat treatment. It can be seen that the heterogeneous gap is reduced.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely exemplary, and those of ordinary skill in the art will appreciate that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

Claims (7)

As a heat treatment method that minimizes the heterogeneous gap of die casting materials applied to automobile engines,
A first heat treatment step of heating a first member made of cast iron before inserting it into a mold to generate a compound containing oxygen on at least a portion of a surface of the first member; And
Including; by inserting the first member into the mold and then performing aluminum die casting, forming a second member that contacts at least a portion of the first member and fixes the first member; and
The separation distance between the interface of the first member and the second member is 10㎛ to 35㎛,
Heat treatment method for minimizing the gap between die casting materials. The method of claim 1,
The first heat treatment is performed in a temperature range of 200 ℃ to 800 ℃,
Heat treatment method for minimizing the gap between die casting materials. The method of claim 2,
In the first heat treatment, the first member is heated to the temperature range and then cooled to room temperature,
Heat treatment method for minimizing the gap between die casting materials. The method of claim 1,
The first heat treatment is performed for 0.5 to 1.5 hours,
Heat treatment method for minimizing the gap between die casting materials. The method of claim 1,
After the first heat treatment step,
Performing a second heat treatment step of reheating the first member,
Heat treatment method for minimizing the gap between die casting materials. The method of claim 5,
The second heat treatment is performed in a temperature range of 100 ℃ to 250 ℃,
Heat treatment method for minimizing the gap between die casting materials. The method of claim 5,
The second heat treatment is performed for 0.5 to 1.5 hours,
Heat treatment method for minimizing the gap between die casting materials.

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