Method for predicting hot crack area of aluminum alloy part

Abstract

The invention provides a method for predicting a hot crack area of an aluminum alloy part, which comprises the following steps: S1, in the solidification and cooling process of an aluminum alloy casting, calculating the stress distribution when the temperature of the aluminum alloy casting reaches the solidus temperature; s2, calculating the strain when the temperature of the aluminum alloy casting reaches the position near the solidus temperature, and obtaining an area with the strain larger than 0; s3, measuring the yield strength near the solidus temperature of the attached casting sample of the aluminum alloy casting by using an experimental means; s4, aiming at each position of the aluminum alloy casting, comparing the stress in the S1 with the yield strength in the S3 to obtain an area of which the stress is greater than the yield strength; and S5, comparing the area obtained in the S2 with the area obtained in the S4 to obtain an overlapped area of the two areas, namely the hot crack area of the aluminum alloy casting. The method has the beneficial effects that the stress, the strain and the yield strength of the aluminum alloy casting are comprehensively considered according to the definition of the hot crack, the considered factors are more comprehensive, the prediction of the hot crack area is more accurate, the reference value provided for process optimization is greater, and the cost is saved.

Description

Technical Field

[0001] The invention belongs to the field of thermal crack prediction of aluminum alloy parts, and in particular relates to a method for predicting the thermal crack area of ​​an aluminum alloy part. Background Art

[0002] At present, the application of aluminum alloy castings will become more and more extensive. Before the application of aluminum alloy castings, the casting process must be analyzed to determine the location of defects such as shrinkage and thermal cracking, so as to optimize the structure and improve the yield of castings.

[0003] At the end of solidification or shortly after solidification, the strength and plasticity of the casting are very low, the casting shrinks in the solid state, and the mold hinders shrinkage. When the stress generated by the shrinkage is greater than the yield strength of the casting at this time, the casting cracks, and the cracks formed are called hot cracks. From the definition of hot cracks, it can be seen that the occurrence of hot cracks is related to the stress, strain and yield strength of the casting. To accurately determine the hot crack area, the stress, strain and yield strength of the casting must be considered comprehensively.

[0004] At present, the common hot cracking criteria are HTI, HCS and CSC. HTI refers to the measurement of the hot cracking sensitivity at each node by calculating the total strain of the solid phase fraction between 50% and 99% of each node of the casting. HCS refers to the hot cracking sensitivity coefficient, which is related to the shrinkage factor, viscosity of the alloy liquid, secondary dendrite spacing, temperature gradient, solidus temperature, melting heat, solid phase fraction, alloy liquid flow rate, alloy deformation rate, and pressure on the hot cracking nucleus. CSC uses the ratio of the non-compensable solidification time fraction to the compensable solidification time fraction to judge the hot cracking tendency of non-directional solidification alloys. It can be seen that the HTI criterion only considers strain, and the HCS criterion has many parameters. For some modified alloys or new grades of alloys, it is difficult to determine all parameters in a short time. The CSC criterion only considers compensation. The three common criteria do not comprehensively consider stress strain and the mechanical properties of the bulk material.

[0005] Finding an efficient, accurate and widely applicable prediction method for hot cracking region is of great significance for the industrial application of aluminum alloy castings, and it has always been a research hotspot. However, the prior art does not involve a prediction method for hot cracking region that comprehensively considers stress, strain and mechanical properties of the main material, and the content of the present invention cannot be derived based on the prior art. Summary of the invention

[0006] In view of this, the present invention aims to propose a prediction method for the hot cracking area of ​​aluminum alloy castings that comprehensively considers stress, strain and mechanical properties of the base material, so as to solve at least one problem existing in the above-mentioned prior art.

[0007] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A method for predicting the hot cracking region of an aluminum alloy part comprises the following steps:

[0009] S1. During the solidification and cooling process of aluminum alloy castings, calculate the stress distribution when the temperature of the aluminum alloy castings reaches the solidus temperature;

[0010] S2. Calculate the strain of the aluminum alloy casting when the temperature reaches the solidus temperature, and obtain the area where the strain is greater than 0;

[0011] S3. Determine the yield strength of the aluminum alloy casting near the solidus temperature by experimental means;

[0012] S4, for each position of the aluminum alloy casting, comparing the stress of step S1 with the yield strength of step S3, and obtaining an area where the stress is greater than the yield strength;

[0013] S5. Compare the area obtained in step S2 with the area obtained in step S4 to obtain the overlapping area of ​​the two, that is, the hot cracking area of ​​the aluminum alloy casting.

[0014] Furthermore, in step S1, the manufacturing process of the aluminum alloy casting is to pour the aluminum alloy liquid metal into a mold, and the liquid metal cools and solidifies in the mold to form a casting. When it is about to solidify or has just solidified, the aluminum alloy solid phase continues to cool, expands due to heat, and contracts due to cold, and the solid phase continues to shrink, resulting in thermal cracking.

[0015] Furthermore, in step S1, the solidification and cooling process of the aluminum alloy casting is a process, and the aluminum alloy casting is processed within a time range determined according to the structure of the casting, the type of aluminum alloy, and the production efficiency.

[0016] Furthermore, in step S1, the software used to calculate the stress distribution when the temperature of the aluminum alloy casting reaches near the solidus temperature is ProCAST or Magma or Abaqus.

[0017] Further, in step S2, the strain is greater than 0, indicating that the aluminum alloy casting is deformed.

[0018] Furthermore, in step S4, based on the stress, strain and bulk material properties of the aluminum alloy casting, step S2 obtains the area where the strain is greater than 0 from the perspective of strain calculation, and step S4 obtains the area where the strain is greater than 0 from the perspective of mechanical properties. The combination of step S2 and step S4 can fit the definition of hot cracking and improve the accuracy of the prediction results.

[0019] Compared with the prior art, the method for predicting the hot cracking area of ​​an aluminum alloy part described in the present invention has the following advantages:

[0020] (1) The method for predicting the hot cracking zone of an aluminum alloy part described in the present invention comprehensively considers the stress, strain and yield strength of the aluminum alloy casting according to the definition of hot cracking, takes more comprehensive factors into consideration, and predicts the hot cracking zone more accurately, providing a greater reference value for process optimization and saving costs.

[0021] (2) The method for predicting the hot cracking area of ​​an aluminum alloy part described in the present invention fully utilizes existing technical means, such as calculation methods of stress and strain, and does not require new formulas or new theories, making it easy to understand and use.

[0022] (3) The method for predicting the hot cracking area of ​​an aluminum alloy part described in the present invention can obtain the yield strength of an aluminum alloy casting sample near the solidus temperature by high-temperature tensile test. The data is easy to obtain and the instrument is common. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 A schematic diagram of a prediction method according to an embodiment of the present invention;

[0025] Figure 2 A schematic diagram of stress distribution near the solidus line of an aluminum-copper alloy body according to an embodiment of the present invention;

[0026] Figure 3 A schematic diagram of a region where the strain near the solidus line of the aluminum-copper alloy body according to an embodiment of the present invention is greater than 0;

[0027] Figure 4 A schematic diagram of a region where the stress is greater than the yield strength according to an embodiment of the present invention;

[0028] Figure 5 A schematic diagram of the hot cracking region of an aluminum-copper alloy body obtained by the method described in an embodiment of the present invention;

[0029] Figure 6 Schematic diagram of the hot cracking area of ​​an aluminum-copper alloy body predicted by the ProCAST software described in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0031] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0032] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0033] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0034] like Figure 1 As shown, a method for predicting the hot cracking area of ​​an aluminum alloy part comprises the following steps:

[0035] S1. During the solidification and cooling process of aluminum alloy castings, calculate the stress distribution when the temperature of the aluminum alloy castings reaches the solidus temperature;

[0036] The manufacturing process of aluminum alloy castings is to pour the molten aluminum alloy into a mold. The molten metal cools and solidifies in the mold to form a casting. When it is about to solidify or has just solidified, the solid phase of the aluminum alloy continues to cool, expands due to heat, and contracts due to cold. The solid phase continues to shrink. If the shrinkage is too large, the solid phase will tear, and thermal cracking will occur at this time.

[0037] In actual use, the solidification and cooling process of aluminum alloy castings refers to a process. Some aluminum alloy castings are processed immediately after they are completely solidified, some are processed after being left for a few hours, and some are processed after being left for a whole day. It needs to be determined according to the casting structure, aluminum alloy type, and production efficiency.

[0038] In this embodiment, stress calculation can be directly calculated using software such as ProCAST, Magma, Abaqus, etc. The main innovation of the present invention is that compared with other technologies, there is no need to learn other theories or manufacture molds.

[0039] In this embodiment, the solidus temperature refers to the temperature at which the alloy solid begins to melt.

[0040] In this embodiment, for the structure of the aluminum alloy casting, the more complex the structure, the easier it is to produce hot cracks. When calculating stress, the lower the temperature that needs to be calculated, the wider the temperature range indicated nearby; the simpler the structure, the less likely it is to produce hot cracks. When calculating stress, the temperature can even be slightly higher than the solidus temperature, and the narrower the temperature range indicated nearby; for the composition of the aluminum alloy, such as aluminum-silicon alloy has good casting performance, the temperature can be calculated to be slightly lower than the solidus temperature when calculating stress, and the narrower the temperature range indicated nearby, while the aluminum-copper alloy has poor casting performance, and the temperature needs to be calculated to be several degrees lower than the solidus temperature when calculating stress, and the wider the temperature range indicated nearby; for different parts of the same aluminum alloy casting, the structures are different, and the temperatures during the solidification process are also different. If the solidus temperature is determined to be ±2°C nearby, it is impossible for every position on the casting to meet the ±2°C requirement. Some slow cooling positions may be ±1°C, and some fast cooling positions may be ±5°C.

[0041] S2. Calculate the strain of the aluminum alloy casting when the temperature reaches the solidus temperature, and obtain the area where the strain is greater than 0;

[0042] In this embodiment, the strain is greater than 0, indicating that deformation has occurred. Thermal cracking is only possible with deformation, and this is the purpose of setting the strain to be greater than 0.

[0043] S3. Determine the yield strength of the aluminum alloy casting near the solidus temperature by experimental means;

[0044] In this embodiment, the experimental method is: according to GB / T 228.3-2015 "Tensile test of metallic materials Part 2: High temperature test method", the yield strength of the cast sample of the aluminum alloy casting near the solidus temperature is measured.

[0045] In this embodiment, yield strength is a technical term, which refers to the yield limit of metal materials when yielding occurs, that is, the stress to resist slight plastic deformation. The reason why this application chooses yield strength is that yield strength is related to deformation, that is, it can be linked to step S2.

[0046] S4, for each position of the aluminum alloy casting, comparing the stress of step S1 with the yield strength of step S3, and obtaining an area where the stress is greater than the yield strength;

[0047] In this embodiment, each position refers to all positions of the aluminum alloy casting.

[0048] In this embodiment, the region where the stress is greater than the yield strength, that is, the region of the aluminum alloy casting cannot withstand such a large stress and deform. Only deformation can cause thermal cracking.

[0049] Step S2 obtains the area where the strain is greater than 0 from the perspective of strain calculation, and step S4 obtains the area where the strain is greater than 0 from the perspective of mechanical properties. Combining step S2 and step S4, the stress, strain and bulk material properties are comprehensively considered, which is more in line with the definition of thermal cracking, and the obtained results are more accurate and more meaningful for reference.

[0050] S5. Compare the area obtained in step S2 with the area obtained in step S4 to obtain the overlapping area of ​​the two, that is, the hot cracking area of ​​the aluminum alloy casting.

[0051] Advantages of the present invention:

[0052] (1) According to the definition of hot cracking, the stress, strain and yield strength of aluminum alloy castings are comprehensively considered. The factors considered are more comprehensive, the prediction of hot cracking zone is more accurate, the reference value provided for process optimization is greater, and cost is saved.

[0053] (2) Existing technical means, such as calculation methods for stress and strain, are fully utilized, without the need for new formulas or new theories, making it easy to understand and use.

[0054] (3) The yield strength of aluminum alloy castings near the solidus temperature can be obtained by high temperature tensile testing. The data is easy to obtain and the instrument is common.

[0055] Example 1

[0056] The aluminum alloy selected is aluminum-copper alloy, with the grade ZL205A.

[0057] The castings selected are diesel engine bodies, which have complex structures and are prone to thermal cracking defects.

[0058] S1. During the solidification and cooling process of the aluminum-copper alloy body, calculate the stress distribution when the temperature of the aluminum-copper alloy body reaches the solidus temperature (such as Figure 2 shown);

[0059] S2. Calculate the strain of the aluminum-copper alloy body when the temperature reaches the solidus temperature and obtain the area where the strain is greater than 0 (such as Figure 3 shown);

[0060] S3. Determine the yield strength (σ) of the aluminum-copper alloy body casting sample near the solidus temperature by means of high temperature tensile test. 0.2 ), σ 0.2 =123MPa;

[0061] S4. For each position of the aluminum-copper alloy body, compare the stress of step S1 with the yield strength of step S3 to obtain the area where the stress is greater than the yield strength (such as Figure 4 shown);

[0062] S5, compare the area obtained in step S2 with the area obtained in step S4, and obtain the overlapping area of ​​the two, that is, the hot cracking area of ​​the aluminum alloy casting (such as Figure 5 shown).

[0063] The hot cracking area of ​​aluminum-copper alloy body is predicted by ProCAST software (such as Figure 6 As shown in the figure, the hot cracking area is compared with the hot cracking area predicted by the method of the present invention. It can be seen from the specific embodiment that compared with the hot cracking area predicted by the commercial software ProCAST, the hot cracking area obtained by the method by comprehensively considering the stress, strain and yield strength of the aluminum alloy casting is more accurate, and the subsequent process optimization is more targeted and less costly.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for predicting the hot cracking area of ​​an aluminum alloy part, characterized in that: The following steps are involved: S1. During the solidification and cooling process of aluminum alloy castings, calculate the stress distribution when the temperature of the aluminum alloy castings reaches the solidus temperature; S2. Calculate the strain of the aluminum alloy casting when the temperature reaches the solidus temperature, and obtain the area where the strain is greater than 0; S3. Determine the yield strength of the aluminum alloy casting near the solidus temperature by experimental means; S4, for each position of the aluminum alloy casting, comparing the stress of step S1 with the yield strength of step S3, and obtaining an area where the stress is greater than the yield strength; S5. Compare the area obtained in step S2 with the area obtained in step S4 to obtain the overlapping area of ​​the two, that is, the hot cracking area of ​​the aluminum alloy casting.

2. The method for predicting the hot cracking region of an aluminum alloy part according to claim 1, characterized in that: In step S1, the manufacturing process of the aluminum alloy casting is to pour the aluminum alloy liquid metal into a mold, and the liquid metal cools and solidifies in the mold to form a casting. When it is about to solidify or has just solidified, the aluminum alloy solid phase continues to cool, expands with heat, and contracts with cold, and the solid phase continues to shrink, resulting in thermal cracking.

3. The method for predicting the hot cracking region of an aluminum alloy part according to claim 1, characterized in that: In step S1, the solidification and cooling process of the aluminum alloy casting is a process, and the aluminum alloy casting is processed within a time range determined according to the structure of the casting, the type of aluminum alloy, and the production efficiency.

4. The method for predicting the hot cracking region of an aluminum alloy part according to claim 1, characterized in that: In step S1, the software used to calculate the stress distribution of the aluminum alloy casting when the temperature reaches the solidus temperature is ProCAST, Magma or Abaqus.

5. The method for predicting the hot cracking region of an aluminum alloy part according to claim 1, characterized in that: In step S2, the strain is greater than 0, indicating that the aluminum alloy casting is deformed.

6. The method for predicting the hot cracking region of an aluminum alloy part according to claim 1, characterized in that: In step S4, based on the stress, strain and bulk material properties of the aluminum alloy casting, step S2 obtains the area where the strain is greater than 0 from the perspective of strain calculation, and step S4 obtains the area where the strain is greater than 0 from the perspective of mechanical properties. The combination of step S2 and step S4 can fit the definition of hot cracking and improve the accuracy of the prediction results.

Images