A die-casting method for improving the density of castings

Abstract

The present invention relates to a die-casting method for improving the density of castings, belonging to the field of aluminum alloy casting technology. The method solves the problems of high porosity, low density, and poor mechanical properties in conventional thick-walled aluminum alloy die-castings. The method comprises the following steps: 1. Adding aluminum alloy raw material to a preheated melting furnace, melting and heating to obtain an aluminum alloy liquid, adding a refining modifier, and stirring; 2. Degassing the aluminum alloy liquid and removing surface scum after standing; 3. Preheating the die-casting mold and spraying a layer of mold release agent; 4. Cooling the aluminum alloy liquid and pouring it into the die-casting mold's inlet gate, which has a thickness of 8 to 12 mm. Using a shot punch, the aluminum alloy liquid is slowly injected into the die-casting mold's cavity; 5. Removing the aluminum alloy die-casting and placing the die-casting in a water tank for quenching to obtain a high-density die-casting. This method achieves the production of high-density aluminum alloy thick-walled die-castings.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy casting, and in particular to a die-casting method for improving the density of castings. Background Art

[0002] Aluminum alloy die-casting technology is suitable for the preparation of metal parts with thin-wall features due to its high-speed filling and high-pressure solidification and shrinkage feeding process characteristics. For thick-walled castings, such as automobile fixing seats and load-bearing bracket parts, the high-pressure shrinkage feeding of traditional die-casting processes cannot completely eliminate shrinkage defects in thick areas of the castings, and the resulting castings have high porosity and low density.

[0003] Existing technologies mainly meet the requirements of low porosity and high toughness for thick-walled aluminum alloy parts by reducing the die-casting speed. However, in actual production, due to the reduction in injection speed, defects such as cold shut, flow marks, and undercasting are easily caused, and problems such as high porosity and high gas content still exist. Summary of the Invention

[0004] In view of the above analysis, the embodiments of the present invention aim to provide a die-casting method for improving the density of castings, so as to solve at least one of the problems of existing aluminum alloy thick-walled die-castings, such as high porosity, low density, and low mechanical properties.

[0005] An embodiment of the present invention provides a die-casting method for improving the density of a casting, comprising the following steps:

[0006] Step 1: adding aluminum alloy metal raw materials into a preheated melting furnace, melting and heating to obtain aluminum alloy liquid, and adding a refining modifier to the aluminum alloy liquid and stirring;

[0007] Step 2: Degas the aluminum alloy liquid prepared in step 1, let it stand and then remove the surface scum;

[0008] Step 3: preheat the die-casting mold and evenly spray a layer of release agent on the inner surface of the die-casting mold cavity;

[0009] Step 4: Cool the aluminum alloy liquid treated in step 2 and pour it into the inlet gate of the die-casting mold treated in step 3. The inlet gate thickness is 8 to 12 mm. Use a shot punch to slowly inject the aluminum alloy liquid into the cavity of the die-casting mold.

[0010] Step 5: Open the die-casting mold, take out the aluminum alloy die-casting from the cavity, and place the die-casting in a water tank for quenching to obtain a high-density die-casting.

[0011] Furthermore, in step 1, the composition of the aluminum alloy components is as follows in mass percentage: Si: 11-13.5%, Cu: 0.5-1.3%, Mg: 0.8-1.2%, Ni: 0.5-1.3%, Mn: 0.01-0.05%, Ti: 0.01-0.05%, Fe: 0.02-1.0%, and the rest is Al.

[0012] Preferably, in step 1, the aluminum alloy metal raw material is melted and heated to 710-730°C.

[0013] It should be noted that in step 1, the refining modifier is a mixture of aluminum-titanium-boron master alloy and aluminum-strontium master alloy, and the aluminum-titanium-boron master alloy and the aluminum-strontium master alloy each account for 0.1-0.4% of the total mass of the alloy.

[0014] Illustratively, in step 2, degassing is performed using rotary blowing of argon.

[0015] Specifically, the degassing time is 20-30 minutes, the argon flow rate is 1-5 L / min, and the mixture is left to stand for 20-30 minutes.

[0016] Furthermore, the preheating temperature of the die-casting mold in step 3 is 150-200°C.

[0017] Preferably, in step 4, the aluminum alloy liquid is cooled to 670-690°C.

[0018] Furthermore, in step 4, the injection speed is 0.05-1.2 m / s, the casting pressure is 110-150 MPa, and the holding time is 2-10 s.

[0019] Furthermore, in step 5, the quenching temperature is 30-60°C.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The present invention achieves grain refinement and Si morphology modification by adding aluminum-titanium-boron master alloy and aluminum-strontium master alloy refiners during the aluminum alloy smelting process and controlling the added amount, so that the eutectic silicon is transformed from coarse needle-like flakes to fine fibers, which plays a metamorphic role. Grain refinement can reduce the gaps between grains, increase the density of the material, meet the density requirements required for subsequent heat treatment, and enhance the strength and plasticity of the alloy.

[0022] 2. The present invention uses a rotary argon injection method to degas the aluminum alloy liquid, effectively reducing the gas content in the aluminum alloy liquid, avoiding defects such as pores and shrinkage cavities in the aluminum alloy liquid during the die-casting process, and effectively improving the density of the die-casting parts.

[0023] 3. The die-casting process of the present invention adopts a relatively high casting pressure (110-150 MPa) combined with a relatively large gate thickness ratio (0.5-1.2), which effectively feeds the thermal section of the casting and significantly improves the density of the casting.

[0024] 4. The present invention optimizes the composition of alloy elements, and the alloy composition is within the range of Al-Si alloy eutectic, with low viscosity and good fluidity. It can better fill the internal holes of the casting in the later stage of casting solidification, which helps to reduce shrinkage cavities and shrinkage defects in the casting; and when the alloy transforms from liquid to solid, α-Al and Si phases are formed at the same time, which is beneficial to improve the mechanical properties of the alloy.

[0025] 5. The present invention solves the problems of shrinkage and shrinkage cavities that are often prone to thick-walled aluminum alloy die-castings by optimizing the elemental composition and die-casting mold, adding an appropriate amount of refining modifier, and combining with higher casting pressure. This improves the density of aluminum alloy die-castings, meets the requirements of T6 and T7 heat treatment, and enables aluminum alloy die-castings to meet service requirements. The aluminum alloy die-castings produced by the present invention have a dense structure, low porosity, and excellent strength and plasticity indicators after heat treatment, with a tensile strength of ≥400 MPa, a yield strength of ≥330 MPa, and an elongation of ≥4%.

[0026] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0028] Figure 1 This is a microstructure diagram of the die casting prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0030] A specific embodiment of the present invention discloses a die-casting method for improving the density of a casting, comprising the following steps:

[0031] Step 1: adding aluminum alloy metal raw materials into a preheated melting furnace, melting and heating to obtain aluminum alloy liquid, and adding a refining modifier to the aluminum alloy liquid and stirring;

[0032] Step 2: Degas the aluminum alloy liquid prepared in step 1, let it stand and then remove the surface scum;

[0033] Step 3: preheat the die-casting mold and evenly spray a layer of release agent on the inner surface of the die-casting mold cavity;

[0034] Step 4: Cool the aluminum alloy liquid treated in step 2 and pour it into the inlet gate of the die-casting mold treated in step 3. The inlet gate thickness is 8 to 12 mm. Use a shot punch to slowly inject the aluminum alloy liquid into the cavity of the die-casting mold.

[0035] Step 5: Open the die-casting mold, take out the aluminum alloy die-casting from the cavity, and place the die-casting in a water tank for quenching to obtain a high-density die-casting.

[0036] Furthermore, in step 1, the composition of the aluminum alloy components is as follows in mass percentage: Si: 11-13.5%, Cu: 0.5-1.3%, Mg: 0.8-1.2%, Ni: 0.5-1.3%, Mn: 0.01-0.05%, Ti: 0.01-0.05%, Fe: 0.02-1.0%, and the rest is Al.

[0037] The following is a detailed description of the effects and dosage of the components in the present invention:

[0038] Si: Forms primary and eutectic Si in the microstructure, ensuring the alloy's wear resistance and fluidity. The added amount should be within the eutectic range of Al-Si alloys. The preferred Si content is 11-13.5%.

[0039] Cu and Ni: Cu and Ni form the Al7Cu4Ni phase, improving the alloy's high-temperature properties. Excessive additions reduce the alloy's elongation. Optimum Cu content is 0.5-1.3%, and Ni content is 0.5-1.3%.

[0040] Mg: Forms the Mg2Si phase, which forms a dispersed Mg2Si strengthening phase during heat treatment, improving the alloy's strength and plasticity. Excessive addition reduces the alloy's elongation. The preferred Mg content is 0.8-1.2%.

[0041] Mn: Improves the Fe phase morphology. Excessive addition forms a Mn-rich second phase, which reduces alloy properties. The preferred Mn content is 0.01-0.05%.

[0042] Ti: Refines the grain structure. Too much Ti will form a coarse Ti-rich phase, which will reduce the alloy properties. The preferred Ti content is 0.01-0.05%.

[0043] Fe: Reduces the tendency to stick to the mold. Excessive addition reduces the elongation of the alloy. The preferred Fe content is 0.02-1.0%.

[0044] Depend on Figure 1 It can be seen that the microstructure after die casting is fine and dense, the α-Al phase in the structure presents a fine dendritic morphology, the average grain size is 30-50 μm, and there is a high area fraction of short rod-shaped eutectic Si phase at the grain boundary, which provides the alloy with better fluidity. At the same time, since the Si content is in the eutectic range, there is a blocky primary Si phase in the structure, which can improve the wear resistance of the alloy.

[0045] Preferably, in step 1, the aluminum alloy metal raw material is melted and heated to 710-730°C.

[0046] Illustratively, in step 1, the refining modifier is a mixture of an aluminum-titanium-boron master alloy and an aluminum-strontium master alloy, with the aluminum-titanium-boron master alloy and the aluminum-strontium master alloy each accounting for 0.1-0.4% of the total alloy mass, with no restriction on the ratio of addition between the two. Specifically, the aluminum-titanium-boron master alloy is added in amounts of 0.1%, 0.2%, 0.3%, and 0.4% of the total alloy mass; and the aluminum-strontium master alloy is added in amounts of 0.1%, 0.2%, 0.3%, and 0.4% of the total alloy mass.

[0047] The aluminum-titanium-boron master alloy comprises Al5TiB, with an addition amount of 0.1-0.4%. After addition, Al3Ti and TiB2 are formed in the melt, which can serve as grain nucleation points and play a role in refining grains. Excessive addition will form coarse Al3Ti phases and reduce the mechanical properties of the alloy.

[0048] The composition of aluminum strontium master alloy is Al10Sr, and the addition amount is 0.1-0.4%. After addition, Sr atoms can inhibit the growth of Si phase and cause the Si morphology to undergo a fiberization transformation, that is, from coarse needle-like to fine fiber-like, which plays a deteriorating role. If too much is added, the deterioration effect will not continue to improve.

[0049] By adding two kinds of refiners, aluminum-titanium-boron master alloy and aluminum-strontium master alloy, grain refinement and Si morphology modification can be achieved. Grain refinement can reduce the gaps between grains, increase the density of the material, and thus improve the strength and plasticity of the alloy.

[0050] Furthermore, in step 2, degassing is performed by rotary blowing of argon, the degassing time is 20-30 minutes, the argon flow rate is 1-5L / min, and the mixture is allowed to stand for 20-30 minutes; the introduction of argon can effectively reduce the gas content in the aluminum alloy liquid, thereby improving the mechanical properties of the aluminum alloy; through the rotary blowing method, the argon gas can be broken into fine bubbles, and the bubbles carry away the gas and slag in the aluminum liquid during the rising process, thereby achieving the purpose of purifying the aluminum liquid.

[0051] It is worth noting that in step 3, the preheating temperature of the die-casting mold is 150-200°C.

[0052] Improper mold temperature setting will affect the performance of the casting. Too low a temperature will lead to difficulty in casting molding, incomplete filling and cold shut defects; too high a temperature will cause defects such as bubbles, sticking and shrinkage holes on the casting surface, and reduce the service life of the mold.

[0053] Specifically, in step 4, the aluminum alloy liquid is cooled to 670-690°C.

[0054] Furthermore, in step 4, the thickness of the gate of the die-casting mold is 8 to 12 mm. The average wall thickness of the die-casting part is 8 to 20 mm.

[0055] For example, in step 4, the injection speed is 0.05-1.2 m / s, the casting pressure is 110-150 MPa, and the holding time is 2-10 s. Specifically, the injection speed is 0.05 m / s, 0.1 m / s, 0.15 m / s, 0.2 m / s, 0.5 m / s, 0.8 m / s, 1 m / s, and 1.2 m / s; and the casting pressure is 110 MPa, 120 MPa, 130 MPa, 140 MPa, and 150 MPa.

[0056] Higher casting pressure (110-150MPa) combined with a larger gate thickness ratio (0.5-1.2) can effectively feed the hot zone of the casting and significantly improve the density of the casting. The alloy composition is close to the Al-Si eutectic and has better fluidity, which can better feed the internal pores of the casting in the later stage of casting solidification.

[0057] Preferably, in step 5, the quenching temperature is 30-60° C., and the surface hardness of the casting is increased by quenching, thereby reducing wear and corrosion of the casting during use.

[0058] T6 heat treatment refers to complete artificial aging after solution treatment, and is suitable for products that will no longer undergo cold working. T7 heat treatment is stabilization treatment after solution treatment, and is suitable for products whose strength exceeds the peak point during artificial aging. Both heat treatments require the alloy to have a certain density to ensure that excessive pore expansion or other defects will not be generated during the heat treatment process, thereby ensuring the mechanical properties and dimensional stability of the alloy.

[0059] In summary, the present invention solves the problems of shrinkage porosity and shrinkage cavities that are often prone to occur in thick-walled aluminum alloy die-castings, thereby improving the density of aluminum alloy die-castings, meeting the requirements of T6 and T7 heat treatments, and ensuring that the aluminum alloy die-castings meet the requirements for use. The aluminum alloy die-castings produced by the present invention have a dense structure and low porosity, and have excellent strength and plasticity indicators after heat treatment, with a tensile strength of ≥400 MPa, a yield strength of ≥330 MPa, and an elongation of ≥4%.

[0060] The die-casting method for improving the density of castings of the present invention will be described below with reference to specific embodiments.

[0061] Example 1

[0062] This embodiment provides a die-casting method for improving the density of castings.

[0063] The aluminum alloy composition is calculated in mass percentage as follows: Si: 12.4%, Cu: 1.1%, Mg: 1.0%, Ni: 0.5%, Mn: 0.05%, Ti: 0.04%, Fe: 0.3%, and the rest is Al, as shown in Table 1.

[0064] The average wall thickness of the casting is 10mm.

[0065] The molding method comprises the following steps:

[0066] Step 1: adding aluminum alloy metal raw materials into a preheated melting furnace to melt the aluminum alloy metal raw materials and heating them to 730° C. to obtain aluminum alloy liquid;

[0067] Step 2: adding a refinement modifier to the aluminum alloy liquid obtained in step 1, and then stirring the aluminum alloy liquid and the refinement modifier together;

[0068] The refining modifier is aluminum-titanium-boron master alloy and aluminum-strontium master alloy, wherein the addition amount of aluminum-titanium-boron accounts for 0.1% of the total mass of the alloy, and the aluminum-strontium master alloy accounts for 0.4% of the total mass of the alloy;

[0069] Step 3: Degas the aluminum alloy liquid prepared in step 2 by rotating argon injection. The degassing time is 20 minutes, the argon flow rate is 3 L / min, and the mixture is allowed to stand for 20 minutes. After standing, the surface scum is removed.

[0070] Step 4: Preheat the die-casting mold to 180°C, and spray a layer of release agent on the inner surface of the die-casting mold cavity;

[0071] Step 5: Cool the aluminum alloy liquid in the smelting furnace to 690°C and pour it into the inlet gate of the die-casting mold. The mold inlet gate thickness is 10 mm (the gate thickness ratio is 1). Use a shot punch to slowly inject the aluminum alloy liquid into the cavity of the die-casting mold; the slow injection speed is 0.1 m / s, the casting pressure is 110 MPa, and the holding time is 8 s.

[0072] Step 6: Open the die-casting mold, then take out the aluminum alloy die-casting from the cavity, and place the die-casting in a water tank for quenching at a quenching temperature of 50° C. to obtain a high-density die-casting.

[0073] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0074] Example 2

[0075] This embodiment provides a die-casting method for improving the density of castings.

[0076] The aluminum alloy composition is calculated in mass percentage as follows: Si: 12.9%, Cu: 1.3%, Mg: 1.0%, Ni: 1.2%, Mn: 0.05%, Ti: 0.05%, Fe: 0.3%, and the rest is Al, as shown in Table 1.

[0077] The average wall thickness of the casting is 12mm.

[0078] The molding method comprises the following steps:

[0079] Step 1: adding aluminum alloy metal raw materials into a preheated melting furnace to melt the aluminum alloy metal raw materials and heating them to 730° C. to obtain aluminum alloy liquid;

[0080] Step 2: adding a refinement modifier to the aluminum alloy liquid obtained in step 1, and then stirring the aluminum alloy liquid and the refinement modifier together;

[0081] The refining modifier is aluminum-titanium-boron master alloy and aluminum-strontium master alloy, wherein the addition amount of aluminum-titanium-boron accounts for 0.2% of the total mass of the alloy, and the aluminum-strontium master alloy accounts for 0.4% of the total mass of the alloy;

[0082] Step 3: Degas the aluminum alloy liquid prepared in step 2 by rotating argon injection. The degassing time is 30 minutes, the argon flow rate is 1 L / min, and the liquid is allowed to stand for 30 minutes. After standing, the surface scum is removed.

[0083] Step 4: Preheat the die-casting mold to 180°C, and spray a layer of release agent on the inner surface of the die-casting mold cavity;

[0084] Step 5: Cool the aluminum alloy liquid in the smelting furnace to 670°C and pour it into the inlet gate of the die-casting mold. The mold inlet gate thickness is 8 mm (the gate thickness ratio is 0.67). Use a shot punch to slowly inject the aluminum alloy liquid into the cavity of the die-casting mold; the slow injection speed is 0.1 m / s, the casting pressure is 130 MPa, and the holding time is 8 s.

[0085] Step 6: Open the die-casting mold, then take out the aluminum alloy die-casting from the cavity, and place the die-casting in a water tank for quenching at a quenching temperature of 50° C. to obtain a high-density die-casting.

[0086] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0087] Example 3

[0088] This embodiment provides a die-casting method for improving the density of castings.

[0089] The composition of the aluminum alloy is in percentage by mass: Si: 11.6%, Cu: 1.0%, Mg: 0.9%, Ni: 1.0%, Mn: 0.05%, Ti: 0.05%, Fe: 0.3%, and the rest is Al, as shown in Table 1.

[0090] The average wall thickness of the casting is 16mm.

[0091] The molding method comprises the following steps:

[0092] Step 1: adding aluminum alloy metal raw materials into a preheated melting furnace to melt the aluminum alloy metal raw materials and heating them to 730° C. to obtain aluminum alloy liquid;

[0093] Step 2: adding a refinement modifier to the aluminum alloy liquid obtained in step 1, and then stirring the aluminum alloy liquid and the refinement modifier together;

[0094] The refining modifier is aluminum-titanium-boron master alloy and aluminum-strontium master alloy, wherein the addition amount of aluminum-titanium-boron accounts for 0.3% of the total mass of the alloy, and the aluminum-strontium master alloy accounts for 0.3% of the total mass of the alloy;

[0095] Step 3: Degas the aluminum alloy liquid prepared in step 2 by rotating argon injection. The degassing time is 30 minutes, the argon flow rate is 1 L / min, and the liquid is allowed to stand for 30 minutes. After standing, the surface scum is removed.

[0096] Step 4: Preheat the die-casting mold to 180°C, and spray a layer of release agent on the inner surface of the die-casting mold cavity;

[0097] Step 5: Cool the aluminum alloy liquid in the smelting furnace to 670°C and pour it into the inlet gate of the die-casting mold. The mold inlet gate thickness is 10 mm (the gate thickness ratio is 0.63). Use a shot punch to slowly inject the aluminum alloy liquid into the cavity of the die-casting mold; the slow injection speed is 0.06 m / s, the casting pressure is 150 MPa, and the holding time is 8 s.

[0098] Step 6: Open the die-casting mold, then take out the aluminum alloy die-casting from the cavity, and place the die-casting in a water tank for quenching at a quenching temperature of 50° C. to obtain a high-density die-casting.

[0099] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0100] Comparative Example 1

[0101] This embodiment provides a die-casting method for improving the density of castings.

[0102] The aluminum alloy composition is calculated in mass percentage as follows: Si: 8.9%, Cu: 1.1%, Mg: 0.9%, Ni: 0.7%, Mn: 0.05%, Ti: 0.05%, Fe: 0.3%, and the rest is Al, as shown in Table 1.

[0103] The molding method is the same as that in Example 1.

[0104] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0105] Comparative Example 2

[0106] This embodiment provides a die-casting method for improving the density of castings.

[0107] The composition of the aluminum alloy is in percentage by mass: Si: 11.2%, Cu: 0.1%, Mg: 0.9%, Ni: 1.1%, Mn: 0.02%, Ti: 0.03%, Fe: 0.2%, and the rest is Al, as shown in Table 1.

[0108] The molding method is the same as that in Example 1.

[0109] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0110] Comparative Example 3

[0111] This embodiment provides a die-casting method for improving the density of castings.

[0112] The composition of the aluminum alloy is in percentage by mass: Si: 10.2%, Cu: 0.6%, Mg: 2.9%, Ni: 0.8%, Mn: 0.02%, Ti: 0.03%, Fe: 0.5%, and the rest is Al, as shown in Table 1.

[0113] The molding method is the same as that in Example 1.

[0114] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0115] Comparative Example 4

[0116] This embodiment provides a die-casting method for improving the density of castings.

[0117] The composition of the aluminum alloy is the same as that of Example 1 in terms of mass percentage.

[0118] The molding method is basically the same as that of Example 1, except that in step 5, the thickness of the gate of the die-casting mold is 4 mm (the gate thickness ratio is 0.4).

[0119] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0120] Comparative Example 5

[0121] This embodiment provides a die-casting method for improving the density of castings.

[0122] The composition of the aluminum alloy is the same as that of Example 1 in terms of mass percentage.

[0123] The forming method is basically the same as that of Example 1, except that in step 2, the amount of aluminum, titanium and boron added is 0.03% of the total mass of the alloy, and the aluminum strontium master alloy is 0.01% of the total mass of the alloy.

[0124] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0125] Comparative Example 6

[0126] This embodiment provides a die-casting method for improving the density of castings.

[0127] The composition of the aluminum alloy is the same as that of Example 1 in terms of mass percentage.

[0128] The molding method is basically the same as that of Example 1, except that in step 5, the slow injection speed is 0.1 m / s, the casting pressure is 60 MPa, and the holding time is 5 s.

[0129] The yield strength, tensile strength and elongation of aluminum alloy die castings after T6 heat treatment were measured according to the test standard GB / T228.1-2021. The results are shown in Table 2.

[0130] Table 1 Aluminum alloy composition and mass percentage (wt%) of the embodiment and comparative example

[0131] serial number Si Cu Mg Ni Mn Ti Fe Example 1 12.4 1.1 1.0 0.5 0.05 0.04 0.3 Example 2 12.9 1.3 1.0 1.2 0.05 0.05 0.3 Example 3 11.6 1.0 0.9 1.0 0.05 0.05 0.3 Comparative Example 1 8.9 1.1 0.9 0.7 0.05 0.05 0.3 Comparative Example 2 11.2 0.1 0.9 1.1 0.02 0.03 0.2 Comparative Example 3 10.2 0.6 2.9 0.8 0.02 0.03 0.5 Comparative Example 4 12.4 1.1 1.0 0.5 0.05 0.04 0.3 Comparative Example 5 12.4 1.1 1.0 0.5 0.05 0.04 0.3 Comparative Example 6 12.4 1.1 1.0 0.5 0.05 0.04 0.3

[0132] Table 2 Mechanical properties of aluminum alloy die castings after heat treatment in Example and Comparative Example

[0133]

[0134]

[0135] The alloy composition of Examples 1 to 3 of the present invention meets the requirements of the present invention. The aluminum alloy die-castings produced by the die-casting method of the present invention have excellent strength and plasticity indicators after heat treatment, with a tensile strength of ≥400 MPa, a yield strength of ≥330 MPa, and an elongation of ≥4%, indicating that the aluminum alloy die-castings produced by the die-casting method of the present invention have low porosity and high density.

[0136] In Comparative Example 1, the Si element content is low, the fluidity of the aluminum alloy liquid after melting is reduced, the shrinkage feeding effect during the solidification process of the casting is poor, and the mechanical properties of the casting after heat treatment are reduced; the Cu element content in Comparative Example 2 does not meet the requirements of the present invention, and the Mg element content in Comparative Example 3 does not meet the requirements of the present invention; in Comparative Example 4, the thickness of the die-casting mold inlet gate is small, and the inlet gate thickness and gate thickness ratio do not meet the requirements of the present invention, which is not conducive to providing more metal liquid to feed the shrinkage inside the casting during the solidification process of the casting; the amount of refining modifier added in Comparative Example 5 is small, and grain refinement cannot be achieved; the casting pressure in Comparative Example 6 is low, and the solidification shrinkage feeding effect is poor; all of these lead to a decrease in the mechanical properties of the casting.

[0137] In summary, the present invention solves the problems of shrinkage porosity, shrinkage cavities and other defects that are often prone to occur in thick-walled aluminum alloy die-castings, thereby improving the density of the aluminum alloy die-castings, meeting the requirements of subsequent heat treatment, and enabling the aluminum alloy die-castings to meet the use requirements; the aluminum alloy die-castings produced by the present invention have a dense structure and low porosity, and have excellent strength and plasticity indicators after heat treatment, with a tensile strength of ≥400MPa, a yield strength of ≥330MPa, and an elongation of ≥4%.

[0138] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A die-casting method for improving the density of castings, characterized in that: The following steps are involved: Step 1: Add aluminum alloy metal raw material into a preheated melting furnace, melt and heat to obtain aluminum alloy liquid, and add a refining modifier to the aluminum alloy liquid and stir; the refining modifier is a mixture of aluminum-titanium-boron master alloy and aluminum-strontium master alloy, and the aluminum-titanium-boron master alloy and the aluminum-strontium master alloy each account for 0.1-0.4% of the total mass of the alloy; Step 2: Degas the aluminum alloy liquid prepared in step 1, let it stand and then remove the surface scum; Step 3: preheat the die-casting mold and evenly spray a layer of release agent on the inner surface of the die-casting mold cavity; Step 4: Cool the aluminum alloy liquid treated in step 2 and pour it into the inlet gate of the die-casting mold treated in step 3. The inlet gate thickness is 8-12 mm. The aluminum alloy liquid is slowly injected into the cavity of the die-casting mold using an injection punch; the casting pressure is 120-150 MPa; Step 5: Open the die-casting mold, take out the aluminum alloy die-casting from the cavity, and place the die-casting in a water tank for quenching to obtain a high-density die-casting; The aluminum alloy composition is as follows by mass percentage: Si: 12.4-12.9%, Cu: 0.5-1.3%, Mg: 0.8-1.2%, Ni: 1.0-1.3%, Mn: 0.01-0.05%, Ti: 0.01-0.05%, Fe: 0.02-1.0%, and the rest is Al; After die casting, the microstructure is fine and dense, the α-Al phase in the structure presents a fine dendritic morphology, the average grain size is 30-50 μm, and the eutectic Si phase at the grain boundary is distributed in the form of short rods. Since the Si content is in the eutectic range, there is a blocky primary Si phase in the structure.

2. The method according to claim 1, characterized in that In step 1, the composition of the aluminum alloy is as follows in mass percentage: Si: 12.4-12.9%, Cu: 1.0-1.3%, Mg: 0.8-1.2%, Ni 1.0-1.2%, Mn: 0.01-0.05%, Ti: 0.01-0.05%, Fe: 0.02-1.0%, and the rest is Al.

3. The method according to claim 1, characterized in that In step 1, the aluminum alloy metal raw material is melted and heated to 710-730°C.

4. The method according to claim 1, wherein In step 1, the refining modifier is a mixture of aluminum-titanium-boron master alloy and aluminum-strontium master alloy, and the aluminum-titanium-boron master alloy and the aluminum-strontium master alloy each account for 0.2-0.4% of the total mass of the alloy.

5. The method according to claim 1, wherein In step 2, degassing is performed by rotary blowing of argon.

6. The method according to claim 5, characterized in that The degassing time is 20-30 minutes, the argon flow rate is 1-5 L / min, and the mixture is left to stand for 20-30 minutes.

7. The method according to claim 1, characterized in that The die-casting mold preheating temperature in step 3 is 150-200°C.

8. The method according to claim 1, characterized in that In step 4, the aluminum alloy liquid is cooled to 670-690°C.

9. The method according to claim 1, characterized in that In step 4, the injection speed is 0.05-1.2 m / s, the casting pressure is 130-150 MPa, and the holding time is 2-10 s.

10. The method according to claim 1, characterized in that In step 5, the quenching temperature is 30-60°C.

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