A process for enhancing the strength of steel-aluminum casted joint interface

Abstract

The application provides a process for enhancing the strength of a steel-aluminum casting combination interface, based on a topological optimization method to obtain a porous lattice unit structure with a porosity of 50%-80%, and the obtained porous lattice unit structure meeting the requirements is subjected to regular processing to form a standard unit with regular holes; a plurality of standard units are arranged into a steel-based inlay model monomer with a lattice porous structure, and a plurality of spaced and uniformly arranged steel-based inlay model monomers are connected to the side wall of a steel-based circular ring model to jointly form a steel-based inlay model; and a steel-aluminum casting combination body is obtained after pressure casting according to the obtained steel-based inlay model. The scheme of the application can not only significantly improve the strength of the steel-aluminum casting combination zone, but also accurately control the strength of the steel-aluminum casting combination zone, and compared with the prior art, the steel-aluminum casting combination zone obtained by the application has no obvious boundary at the metallurgical combination interface and has good uniformity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel-aluminum composite component preparation, and particularly relates to a process for enhancing the strength of a steel-aluminum casting joint interface. BACKGROUND

[0002] Typical steel-aluminum casting is stainless steel-aluminum alloy inlay casting, but due to the large differences in thermal expansion coefficient, electrode potential, interface wetting, stress state, etc. between the aluminum matrix and the stainless steel insert, problems such as intermittent interface, non-uniform diffusion, stress accumulation, etc. occur during the filling and solidification process, and brittle intermetallic compounds such as Fe2Al5 are generated, which eventually evolves into serious interface defects such as air gap, hole, crack, etc., thereby damaging the mechanical properties of the steel-aluminum joint interface.

[0003] At present, although the typical steel-aluminum inlay casting technology (such as the steel-aluminum inlay technology in document CN108097927B) has made considerable technical progress, it is difficult to accurately control the strength of the steel-aluminum casting joint area. For example, the bonding interface strength of different parts of the same ring steel-aluminum component can differ by more than 15 MPa.

[0004] Research shows that by pre-treating the surface of the steel insert before pouring, it is beneficial to inhibit the failure behavior of holes, cracks, etc. at the inlay interface and improve the bonding strength, but the metallurgical bonding interface still has a clear demarcation zone (microstructure), which needs to be further optimized and improved. SUMMARY

[0005] One of the purposes of the present application is to provide a process for enhancing the strength of a steel-aluminum casting joint interface.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions.

[0007] A process for enhancing the strength of a steel-aluminum casting joint interface, comprising the following steps:

[0008] Step 1, constructing a steel-based ring model and a digital model unit, and performing mesh division on the digital model unit;

[0009] Step 2, based on the topology optimization method, dividing the digital model unit into a plurality of optimization spaces, and then performing discrete processing to obtain an optimization target;

[0010] Step 3, applying a shear load to the optimization target to obtain a stress-strain cloud map of the digital model unit under the action of the shear load;

[0011] Step 4, analyzing the stress condition of the digital model unit according to the obtained stress-strain cloud map, and carrying out topology optimization to obtain a porous dot array unit structure with a porosity of 50%-80%;

[0012] Step 5, removing the porous lattice unit structure not meeting the filling requirements, and performing a regular treatment on the obtained porous lattice unit structure meeting the requirements to form a standard unit with regular holes;

[0013] Step 6, arranging a plurality of standard units into a steel-based mosaic model monomer with a lattice hole structure, and connecting a plurality of spaced and uniformly arranged steel-based mosaic model monomers to form a steel-based mosaic model together after the steel-based mosaic model monomer is arranged on the side wall of the steel-based ring model;

[0014] Step 7, obtaining a steel-aluminum cast combination through pressure casting according to the obtained steel-based mosaic model.

[0015] As a preferred solution, the porosity of the porous lattice unit structure is 70%.

[0016] As a preferred solution, the material of the steel-based mosaic structure is 316L, and the aluminum alloy is ZL205A alloy; in step 7, the preheating temperature of the mold and the steel base is 500±3℃, the casting pressure is 60±5Kpa, the pouring temperature is 710±5℃, and the pressure holding time is 30±3S.

[0017] As a preferred solution, in step 7, the lattice hole structure is prepared by using a selective laser melting process, and the material used is a powder particle with an average particle size of d50; before the steel-aluminum composite, the steel-based mosaic structure needs to be surface treated.

[0018] As a preferred solution, the size of the digital model unit is 20mm×20mm×20mm, and the grid is divided according to the X, Y and Z three direction reference of 20 layers.

[0019] As a preferred solution, any two adjacent steel-based mosaic model monomers are parallel to each other.

[0020] As a preferred solution, the steel-based mosaic structure is in a whole circular ring structure.

[0021] As a preferred solution, in step 3, after the optimized target is subjected to a shear load, the digital model unit is subjected to topological optimization by using the Ansys software Topology optimization module, the minimum normalized density is 1e -3 , the penalty factor is 6, and the convergence accuracy is 0.001.

[0022] Beneficial effects: by using the scheme of the present application, the strength of the steel-aluminum cast combination area can be significantly improved, the strength of the steel-aluminum cast combination area can be accurately controlled, and the difference between the strengths of different parts of the same circular ring steel-aluminum component is small; compared with the existing scheme, the steel-aluminum cast combination area obtained by using the present application has no obvious boundary and good uniformity. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Schematic diagram of load application mode in step 3 of the embodiment;

[0024] Figure 2 Stress-strain nephogram in the embodiment;

[0025] Figure 3 Schematic diagram of a porous point array unit structure model in the embodiment;

[0026] Figure 4 Schematic diagram of a standard unit with regular holes in the embodiment;

[0027] Figure 5 Schematic diagram of a steel-based inlay model in the embodiment;

[0028] Figure 6 Schematic diagram of a steel-based inlay model in the embodiment (arrangement mode of a single steel-based inlay model);

[0029] Figure 7 Interface structure diagram of steel / aluminum with different porosities in the embodiment. Embodiment

[0030] The technical solutions in the present application will be described clearly and completely below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application. Embodiment

[0031] A process for enhancing the strength of a steel-aluminum cast joint, comprising the steps of:

[0032] Step 1, constructing a steel-based ring model and a digital model unit, and performing mesh division on the digital model unit;

[0033] Specifically, a cube is taken as a basic unit (i.e., a digital model unit), the cube size is 20 mm x 20 mm x 20 mm, a mesh unit with a side length of 1 mm is selected for mesh division, and 20 layers are divided in each of the X, Y and Z directions, so that 8000 units are obtained;

[0034] Step 2, based on a topology optimization method, the digital model unit is divided into a plurality of optimization spaces, and then discrete processing is performed to obtain an optimization target;

[0035] The material properties of the 316L stainless steel corresponding to the digital model unit are a Young's modulus of 187 Gpa and a Poisson's ratio of 0.3;

[0036] Step 3, apply a shear load to the optimization target, and obtain the stress-strain nephogram of the digital model unit under the shear load;

[0037] A load of 100 MPa is applied to the upper half of the left side and the lower half of the right side of the digital model unit, and the eight vertices are fixedly constrained, and the model load is applied as shown in Figure 1 After the basic attribute parameters of the material are input, the mesh is divided, and the load is applied, the digital model unit is topologically optimized by using the Topology optimization module of the Ansys software, the minimum normalized density is 1e -3 , the penalty factor is 6, and the convergence accuracy is 0.001, and the stress-strain nephogram obtained is as shown in Figure 2 ;

[0038] Step 4, according to the stress-strain nephogram, the stress of the digital model unit is analyzed, and the topological optimization is carried out, and a porous point array unit structure with a porosity of 50%-80% is obtained;

[0039] It can be known from the stress nephogram that the stress of the digital model unit at the eight corners is large, and there is a stress concentration phenomenon, and it can be known from the strain nephogram that the strain of the digital model unit at the upper and lower four edges is large, and the strain of the core part is smallest. When the topological optimization is solved, the material at the position with stress concentration and large strain needs to be reserved;

[0040] According to the stress analysis result of the digital model unit, the topological optimization of the digital model unit is carried out, and a porous point array unit structure model with a porosity of 50%, 60%, 70% and 80% is as shown in Figure 3 It can be known from the figure that the material is basically distributed at the position with stress and strain concentration, and when the porosity is 80%, the reserved material after the topological optimization is less, and the support is too thin;

[0041] Step 5, the porous point array unit structure that does not meet the filling requirement is removed (the structure with a porosity of 80% is removed), and the obtained porous point array unit structure that meets the requirement is regularized to form a standard unit with regular holes;

[0042] Considering that the digital model unit will be formed by selective laser forming, the rod diameter is too thin to cause forming difficulty or rod diameter fracture, and in order to reduce the resistance of the molten aluminum melt during filling, it is determined that the porosity of the porous point array unit is 50%, 60% and 70% initially, and after further optimization, it is determined that the porosity of the porous point array unit is 70%;

[0043] There are many irregular surfaces in the porous point array unit obtained after the topological optimization, and the shape is complex. The porous point array unit obtained by the topological optimization is processed to be regular, and a structure with a regular shape is formed, that is, a standard unit with regular holes is formed, as shown inFigure 4 as shown in

[0044] Step 6, arrange several standard units into steel-based mosaic model monomers with dot array pore structure, form a steel-based mosaic model by spacing and uniformly arranging multiple steel-based mosaic model monomers on the sidewall of the steel-based ring model, and make the adjacent two steel-based mosaic model monomers parallel to each other, as shown in Figure 5 and Figure 6

[0045] Through such structure, mechanical interlocking and metallurgical bonding interface between the melt and the steel base can be ensured during casting; based on the steel-based mosaic model monomers obtained through the foregoing topological optimization, different arrangement modes are formed on the surface of the steel-based ring model, and the optimal arrangement mode is determined through Procast simulation analysis, as shown in Figure 5 and Figure 6

[0046] Step 7, according to the obtained steel-based mosaic model, inject molten aluminum alloy into the steel-based mosaic structure, and form a steel-aluminum cast combination after pressure casting.

[0047] The dot array pore structure is prepared by using a selective laser melting process, and the material used is a powder particle with an average particle size of d50.

[0048] Specifically:

[0049] First, the steel base (stainless steel ring with an inner diameter of 1300 mm, an outer diameter of 1400 mm, and a height of 100 mm) is subjected to surface treatment such as alkali washing and acid washing to ensure that the surface of the steel base remains clean; then, the selective laser melting process is used to prepare the dot array pore structure on the surface of the steel base, and the structure obtained at this time corresponds to Figure 5 the model shown; then, pressure casting is performed.

[0050] In the pressure casting process, the mold is preheated in the furnace, immediately placed in the preheated mold after preheating, and the ZL205A alloy melt is quickly injected into the mold to complete the aluminum / steel bimetallic composite; wherein the preheating temperature of the mold and the steel base is 500±3℃, the casting pressure is 60±5Kpa, the pouring temperature is 710±5℃, and the pressure holding time is 30±3S;

[0051] Under the condition that other process parameters remain unchanged, three groups of samples are prepared, the porosity of the dot array pore structure of sample 1 is 50%, the porosity of the dot array pore structure of sample 2 is 60%, and the porosity of the dot array pore structure of sample 3 is 70%.

[0052] Figure 7 ​​Figures (a), (b), (c) are macro-morphologies of steel / aluminum interfaces with porosities of 50%, 60%, and 70% respectively. Under the condition of pressurized casting, the molten aluminum alloy fills the lattice porous structure well, and no macro-defects such as gaps are generated at the steel / aluminum interface, and the bonding effect is good. Figure 7 Figures (a1), (b1), (c1) are microstructures of steel / aluminum interfaces with porosities of 50%, 60%, and 70% respectively. When the porosity is 50%, there is an obvious black gap at the steel / aluminum interface, and the width of the gap is about 8 um. The generation of the gap will affect the bonding effect of the interface and reduce the interface bonding strength. When the porosity is 60%, the gap at the steel / aluminum interface is obviously reduced, and the width of the gap is about 4 um. The interface bonding condition is improved. When the porosity is 70%, the steel / aluminum interface is tightly bonded, and there is no gap phenomenon. The bonding effect is good. The results also show that within a certain porosity range, as the porosity increases, the gap at the interface gradually decreases, and the interface bonding effect gradually improves.

[0053] In the present application, the strength measured is tensile strength. The test results show that when the porosity of the lattice porous structure is 50%, the average strength at the steel / aluminum interface is 78.4 MPa (the maximum strength difference of the six test sites is 5.9 MPa, and the test sites correspond to the positions of 0°, 60°, 120°, 180°, 240°, and 300° on the ring, respectively). When the porosity of the lattice porous structure is 60%, the average strength at the steel / aluminum interface is 96.3 MPa (the maximum strength difference of the six test sites is 4.1 MPa). When the porosity of the lattice porous structure is 70%, the average strength at the steel / aluminum interface is 110.2 MPa (the maximum strength difference of the six test sites is 1.8 MPa). The results also show that within a certain porosity range, the strength at the steel / aluminum interface increases with the increase of the porosity, and especially when the porosity is 70%, there is no gap at the interface. Example

[0054] A steel-based inlay model of the same specification (same outer contour size and material) as in the example is used. After sandblasting treatment (average particle size of sand particles is 3 mm, and the pressure of compressed gas is 0.8 MPa) of the steel model, pressurized casting is carried out while keeping other process parameters unchanged (other process parameters are the same as in the example). The results show that after sandblasting treatment, the bonding condition of the steel / aluminum interface is good, and there are no obvious cracks, pores, porosity, and other defects, but the bonding interface strength is low, and the average strength at the steel / aluminum interface is only about 86.7 MPa. The uniformity of the bonding interface is also poor, and the maximum strength difference of the six test sites reaches 15.4 MPa.

[0055] The solution adopted in this embodiment can not only significantly improve the strength of the steel-aluminum casting interface, but also precisely control the strength of the steel-aluminum casting interface. Taking the prepared circular steel-aluminum component as an example, the strength difference of the bonding area in different parts of the same circular steel-aluminum component is small. Compared with the existing solution, the steel-aluminum casting interface obtained by the present invention has no obvious boundary and good microstructure uniformity.

Claims

1. A process for enhancing the strength of steel-aluminum casted bond interface, characterized by the steps of The application relates to a steel-aluminum cast combination and a preparation method thereof. Step 1, a steel base ring model and a digital model unit are constructed, and the digital model unit is meshed; Step 2, based on a topological optimization method, the digital model unit is divided into a plurality of optimization spaces, then is discretely processed, and an optimization target is obtained; Step 3, a shear load is applied to the optimization target, and a stress-strain nephogram of the digital model unit under the shear load is obtained; wherein, after the shear load is applied to the optimization target, a Topology optimization module in the Ansys software is used to perform topology optimization on the unit body, a minimum normalized density is 1e -3 , a penalty factor is 6, and a convergence accuracy is 0.001; Step 4, the stress-strain nephogram is analyzed to analyze the stress condition of the digital model unit, and topological optimization is carried out to obtain a porous point array unit structure with a porosity of 50%-80%; Step 5, the porous point array unit structure that does not meet the filling requirement is removed, the obtained porous point array unit structure that meets the requirement is regularized to form a standard unit with a regular hole; Step 6, a plurality of standard units are arranged into a steel base inlaid model unit with a point array porosity structure, and a plurality of steel base inlaid model units are arranged at intervals and uniformly on the side wall of the steel base ring model to form a steel base inlaid model; any two adjacent steel base inlaid model units are parallel to each other; the steel base inlaid structure as a whole has a ring structure; Step 7, the obtained steel base inlaid model is pressure cast to obtain the steel-aluminum cast combination; The porosity of the porous point array unit structure is 70%. In step 7, the point array porosity structure is prepared by using a selective laser melting process, the material used is a powder particle with an average particle size of d50, specifically, the steel base is subjected to alkali washing and acid washing surface treatment; then the selective laser melting process is used to prepare the point array porosity structure on the surface of the steel base; then pressure casting is carried out; in the pressure casting process, the mold is preheated in a furnace, immediately placed in the preheated mold after preheating, and the ZL205A alloy melt is quickly injected into the mold to complete the aluminum / steel double metal composite; wherein the preheating temperature of the mold and the steel base is 500+ / -3 DEG C, the casting pressure is 60+ / -5 KPa, the pouring temperature is 710+ / -5 DEG C, and the pressure holding time is 30+ / -3 S.

2. The process for enhancing steel-aluminum casted joint interface strength according to claim 1, wherein, The digital model unit has a size of 20mm*20mm*20mm, and is meshed according to the X, Y and Z three-directional bases.

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