As-cast high-toughness Al-Mg alloy and preparation method thereof

Abstract

The invention provides an as-cast high-toughness Al-Mg alloy and a preparation method thereof, and relates to the field of cast aluminum alloys. The as-cast high-toughness Al-Mg alloy is prepared from the following components in percentage by weight: 6.0%-7.5% of Mg, 2.5%-3.0% of Si, 0.6%-0.8% of Mn, 0.05%-0.1% of Sr, 0.2%-0.4% of Bi, less than or equal to 0.2% of Fe and the balance of Al. The mass ratio of Mg to Si is greater than or equal to 2.3, and the mass ratio of Bi to Sr is greater than or equal to 4. According to the invention, the defects in the prior art are overcome, and the strength and plasticity of the Al-Mg alloy in an as-cast state are remarkably improved, so that the application of the Al-Mg alloy in the fields of automobiles, communication, electronics or aerospace is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of casting aluminum alloy, and particularly relates to a as-cast high strength and toughness Al-Mg alloy and a preparation method thereof. BACKGROUND

[0002] Aluminum alloy gradually replaces cast iron with its higher specific strength, excellent corrosion resistance and other advantages, and is widely used in the fields of automobile and aviation. Under the double driving of the acceleration of new energy vehicle industry and the iteration and upgrading of automobile lightweight technology, the market demand of die-casting aluminum alloy material is expected to continue to rise at an annual compound growth rate of more than 8%, and with the tightening of global carbon emission regulations and the popularization of high-vacuum die-casting process, it further consolidates its position as a core material to achieve the goal of vehicle weight reduction.

[0003] Al-Mg alloy is a kind of aluminum alloy commonly used in die casting, which has excellent corrosion resistance, high specific strength and good weldability, and has attracted more and more attention in recent years. However, the casting performance of this alloy is poor, the mechanical properties are greatly affected by wall thickness, and the hot cracking tendency is serious. In order to expand the application range of Al-Mg alloy, researchers have been committed to developing new casting Al-Mg alloy with reduced hot cracking and improved casting performance by introducing Si element, such as Magsimal-59 (Al-5Mg-2Si-Mn) alloy, which belongs to hypoeutectic Al-Mg2Si alloy. The addition of Si element promotes the formation of eutectic Mg2Si phase, thereby improving the fluidity of the alloy. In addition, a certain amount of manganese (Mn) or iron (Fe) is added to avoid the dissolution of molten aluminum metal and the welding of die steel. However, the eutectic Mg2Si phase contained in this alloy is coarse lamellar and reticular in as-cast state, which seriously cuts the Al matrix, produces stress concentration, forms crack source, and seriously reduces the strength and elongation of the alloy.

[0004] To solve this problem, domestic and foreign researchers improve the morphology of eutectic Mg2Si by adding modifiers, for example: CN119101835A hypoeutectic and eutectic Al-Mg2Si composite material and preparation thereof, which uses Al-Sr-RE composite modifier to modify eutectic Mg2Si, the phase formed by Ce, La and Sr in the Al-Sr-RE composite modifier has a good promoting effect on the growth and twinning transformation of eutectic Mg2Si, and can improve the strength and plasticity of the prepared hypoeutectic and eutectic Al-Mg2Si composite material, but the tensile strength in the gravity casting state is only 180MPa~200MPa, and the elongation is 8%~11.5%, CN108300884A discloses a modification and refinement method of hypoeutectic Al-Mg2Si alloy, which improves the morphology of eutectic Mg2Si phase by adding metal particles Bi, which is easily adsorbed and gathered in front of the growth interface of the first precipitated eutectic phase during the eutectic reaction of Al-Mg2Si, and the eutectic phase is refined and modified, but the tensile strength after modification is only 230MPa~250MPa in the gravity casting state, and the elongation is 6%~10%.

[0005] In the above method, the addition of Si element in the Al-Mg alloy promotes the formation of eutectic Mg2Si phase and improves the casting performance, and accelerates the development of Al-Mg alloy in new energy vehicles and 3C industry, but the coarse eutectic phase affects the comprehensive mechanical properties, although the eutectic Mg2Si is modified by adding Ce, La and Bi elements, the effect is not obvious, and the improvement of the comprehensive mechanical properties is limited, how to improve the strength and plasticity of Al-Mg alloy at the same time has become a hot spot of current research. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a cast high strength and toughness Al-Mg alloy and a preparation method thereof, which significantly improves the strength and plasticity of the Al-Mg alloy in the cast state to meet the application in the fields of automobile, communication, electronics or aerospace.

[0007] To achieve the above object, the present application is realized by the following technical scheme: A cast high strength and toughness Al-Mg alloy, the Al-Mg alloy is composed of the following mass percentage components: Mg: 6.0%~7.5%, Si: 2.5%~3.0%, Mn: 0.6%~0.8%, Sr: 0.05~0.1%, Bi: 0.2~0.4%, Fe≤0.2%, and the balance is Al; and the mass ratio of Mg to Si is ≥2.3, and the mass ratio of Bi to Sr is ≥4.

[0008] The preparation method of the cast high strength and toughness Al-Mg alloy comprises the following steps: S1, pure aluminum, Al-Si intermediate alloy, Al-Mn intermediate alloy is mixed completely melted, then add magnesium block to completely melt, stirring uniform and standing heat preservation, get the first melt for standby; S2, Al-Sr intermediate alloy, pure Bi is added to the first melt, completely melt after stirring uniform and standing heat preservation complete compound modification, get the second melt for standby; S3, the second melt is refined and slagging, and is cast into shape to obtain as-cast Al-Mg alloy castings.

[0009] Preferably, the step S1 Al-Si intermediate alloy is Al-20Si intermediate alloy, Al-Mn intermediate alloy is Al-10Mn intermediate alloy.

[0010] Preferably, the step S1 pure aluminum, Al-Si intermediate alloy, Al-Mn intermediate alloy is mixed completely melted at a temperature of 770-800℃.

[0011] Preferably, the step S1 control the temperature of magnesium block adding ≤740℃, and the magnesium block is wrapped with aluminum foil when adding, and the stirring time is 2-5min, and the standing heat preservation time is 10-20min.

[0012] Preferably, the step S2 Al-Sr intermediate alloy is Al-10Sr intermediate alloy, and pure Bi is added in the form of metal particles.

[0013] Preferably, the step S2 Al-Sr intermediate alloy, pure Bi is added to the first melt at a temperature ≤740℃, and the stirring time is 2-5min, and the standing heat preservation time is 10-20min.

[0014] Preferably, the step S3 is refined and slagging, and the specific way is to add slagging agent to the second melt by argon blowing method, the slagging agent is mixed and matched by the mass ratio of commercially available YT-J-1 refining agent and YT-D-4 refining agent 1:1, the total addition amount is 1% of the weight of the second melt, after refining and slagging, standing for 2-10min, controlling the melt temperature in the range of 720-740℃, then scraping the dross on the surface of the alloy liquid.

[0015] Preferably, the step S3 is cast into shape, and the second melt after refining and slagging is kept at 720-740℃ and cast into a preheated metal mold at 250-300℃ to form.

[0016] The preparation principle is as follows: Si element eutectic transformation occurs after the alloy solidification forming eutectic Mg2Si strengthening phase, the alloy crystallization temperature range is narrowed, the alloy casting performance is improved, and meanwhile, sufficient Mg2Si phase can improve the mechanical strength of the alloy, but the elongation is decreased. Since the mass ratio of Mg and Si is greater than or equal to 2.3, the residual Mg is dissolved in the Al matrix to play a solid solution strengthening effect, but with the increase of the Mg content, the solidification temperature range of the alloy is widened, thereby increasing the hot cracking tendency of the alloy, and excessive Mg and Al form Al8Mg5 and Al3Mg2 phases, which can also reduce the elongation of the alloy casting. Through a large number of experiments, the residual Mg is controlled to be less than 2%.

[0017] Mn is dissolved in the Al matrix to play a solid solution strengthening effect. In addition, when the die casting process is used, Fe and Mn can also play a mold release effect. The addition of Mn can inhibit the formation of β-Fe phase and promote the transformation of β-Fe phase to α-Fe phase. The mechanical properties of the alloy are improved by reducing the cutting of the iron phase to the alloy matrix.

[0018] Bi and Sr elements refine the eutectic Mg2Si strengthening phase. According to the fine-grain strengthening mechanism, the strength and plasticity of the alloy are improved at the same time.

[0019] Compound modification: Bi can promote the nucleation of eutectic Mg2Si by forming Mg3Bi2 compounds with Mg, which has a lattice constant close to Mg2Si, thereby increasing the eutectic nucleation temperature and increasing the eutectic nucleation undercooling to refine the eutectic Mg2Si. The addition amount of Bi element cannot be excessive, and the refining effect will decline when the addition amount exceeds a certain value. Through a large number of experimental studies, the addition amount of Bi element is controlled to be less than 0.4%. Sr is adsorbed and gathered in front of the growth interface of the first precipitated eutectic Mg2Si phase, thereby inhibiting the lateral growth of the eutectic Mg2Si and promoting the twinning transformation of the eutectic Mg2Si, so that the platelet structure is changed into a fibrous structure. In addition, Sr is easy to burn in the aluminum alloy melt, and excessive Sr will not improve the modification effect, but will lead to the precipitation of a large amount of Sr-containing compounds, thereby reducing the mechanical properties of the alloy. Through a large number of experimental studies, the addition amount of Sr is controlled to be less than 0.1%. Bi promotes the nucleation of Bi and the adsorption of modification elements Sr, and the two complement each other, thereby significantly improving the modification and refinement effect of the eutectic Mg2Si. Finally, fine granular eutectic Mg2Si is formed, and the strength and plasticity of the alloy in the as-cast state are greatly improved.

[0020] The present application provides a kind of as-cast high strength and toughness Al-Mg alloy and preparation method thereof, compared with prior art, the advantages are as follows: (1) the as-cast high strength and toughness Al-Mg alloy prepared in the present application has high strength in the as-cast state, which is mainly due to the addition of Si and Mg to form Mg2Si second phase strengthening effect and the residual Mg and a small amount of Mn in the Al matrix to play a solid solution strengthening effect.

[0021] (2) The present application is directed to the coarse lamellar eutectic Mg2Si phase in the as-cast high strength and toughness Al-Mg alloy, through the addition of elements Sr and Bi micro-alloying for refining modification treatment, significantly improving the modification and refinement effect of eutectic Mg2Si, and finally forming fine granular eutectic Mg2Si, and by limiting the mass ratio of Mg and Si ≥ 2.3, the strength and plasticity of the alloy in the as-cast state are greatly improved, and the performance of the final alloy is comprehensively improved.

[0022] (3) The cast aluminum alloy prepared by the present application has high strength and high plasticity in the as-cast state without heat treatment, and the tensile strength is more than 311 MPa and the elongation reaches 22%.

[0023] (4) The cast aluminum alloy prepared by the present application is suitable for various casting methods, and the castings cast from the alloy are expected to be used as structural parts of new lightweight materials in the fields of new energy vehicles and aerospace. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the optical microstructure diagram of the Al-6.0Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy in Example 1; Figure 2 is the optical microstructure diagram of the Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy in Example 2; Figure 3 is the optical microstructure diagram of the Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy in Example 3; Figure 4 is the optical microstructure diagram of the Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy in Example 4; Figure 5 is the optical microstructure diagram of the Al-6.5Mg-2.5Si-0.7Mn alloy in Comparative Example 1; Figure 6 is the optical microstructure diagram of the Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy in Comparative Example 2; Figure 7 is the optical microstructure diagram of the Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy in Comparative Example 3; Figure 8 is the optical microstructure diagram of the Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy in Comparative Example 4.

[0025] Figure 9The optical microstructure diagram of the Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.1Bi alloy in Comparative Example 5. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some embodiments but not all embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0027] Example 1

[0028] Preparation of the Al-6.5Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi (mass content, Mg: 6.5%, Si: 2.5%, Mn: 0.6%, Sr: 0.05%, Bi: 0.2%) alloy: The pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn, Al-10Sr intermediate alloy are used as raw materials for batching, and the Al-6.5Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy melt is prepared by melting, and finally cast into shape. The specific steps and process parameters are as follows: (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy, the pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn, Al-10Sr intermediate alloy raw materials required for preparing the target alloy are calculated and weighed respectively; (2) Alloy melting: the weighed pure aluminum, Al-20Si, Al-10Mn intermediate alloy raw materials are melted in the furnace, the melting temperature is 780℃, after completely melted, the temperature is lowered to 730℃, the pure Mg block wrapped with aluminum foil is added, stirred for 2min, and the composition is uniform and placed for 10min, to obtain the required Al-6.5Mg-2.5Si-0.6Mn alloy melt; (3) Adding micro-alloying elements Sr and Bi: the Al-10Sr intermediate alloy and Bi metal particles are added to the Al-6.5Mg-2.5Si-0.6Mn alloy melt, after completely melted, stirred for 2min, to make the composition uniform, and placed for 10min; (4) Melt refining and slag removal: remove the surface scum of the alloy melt after step (3), control the melt temperature in the range of 720-740 °C, add the slag remover by argon blowing method, the slag remover is mixed by the commercial YT-J-1 refining agent and YT-D-4 refining agent with the mass ratio of 1:1, the total addition amount is 1% of the weight of the second melt, and the standing and heat preservation time is 2 min; (5) Melt casting and forming: control the melt temperature in step (4) at 720 °C, then cast into a metal mold preheated to 250 °C, obtain the Sr and Bi compound modification treated Al-6.5Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy casting, and finally analyze the sample from the casting.

[0029] Example 2:

[0030] Preparation of Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy: (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy, calculate and weigh the required pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn, and Al-10Sr intermediate alloy raw materials for preparing the target alloy; (2) Alloy smelting: melt the weighed pure aluminum, Al-20Si, and Al-10Mn intermediate alloy raw materials in the furnace, the melting temperature is 780 °C, after complete melting, cool to 730 °C, add pure Mg block wrapped with aluminum foil, stir for 2 min, make the composition uniform, and stand and heat preservation for 10 min, obtain the required Al-6.5Mg-2.5Si-0.7Mn alloy melt; (3) Add micro-alloying elements Sr and Bi: add Al-10Sr intermediate alloy and Bi metal particles to the Al-6.5Mg-2.5Si-0.7Mn alloy melt, after complete melting, stir for 2 min, make the composition uniform, and stand and heat preservation for 10 min; (4) Melt refining and slag removal: remove the surface scum of the alloy melt after step (3), control the melt temperature in the range of 720-740 °C, add the slag remover by argon blowing method, the slag remover is mixed by the commercial YT-J-1 refining agent and YT-D-4 refining agent with the mass ratio of 1:1, the total addition amount is 1% of the weight of the second melt, and the standing and heat preservation time is 2 min; (5) Melt casting and forming: control the melt temperature in step (4) at 720 °C, then cast into a metal mold preheated to 250 °C, obtain the Sr and Bi compound modification treated Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy casting, and finally analyze the sample from the casting.

[0031] Example 3:

[0032] Preparation of Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy: (1) Alloy preparation: according to the target composition Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy, the required pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn, Al-10Sr intermediate alloy raw materials for preparing the target alloy were calculated and weighed respectively; (2) Alloy melting: the weighed pure aluminum, Al-20Si, Al-10Mn intermediate alloy raw materials were melted in the furnace, the melting temperature was 780℃, after completely melted, the temperature was lowered to 730℃, the pure Mg block wrapped with aluminum foil was added, stirred for 2min, and the composition was uniform and placed for 10min, to obtain the required Al-7.0Mg-3.0Si-0.7Mn alloy melt; (3) Adding micro-alloying elements Sr and Bi: Al-10Sr intermediate alloy and Bi metal particles were added to the Al-7.0Mg-3.0Si-0.7Mn alloy melt, after completely melted, stirred for 2min, to make the composition uniform, and placed for 10min; (4) Melt refining and slag removal: the alloy melt after melting in step (3) was removed from the surface dross, the melt temperature was controlled in the range of 720℃~740℃, the slag remover was added by argon blowing method, the slag remover was mixed by the mass ratio of 1:1 of commercially available YT-J-1 refining agent and YT-D-4 refining agent, the total addition amount was 1% of the second melt weight, and the temperature was kept for 2min; (5) Melt casting forming: the melt temperature in step (4) was controlled at 720℃, then cast into a metal mold preheated to 250℃, to obtain Sr and Bi composite modification Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy castings, and finally the castings were sampled and analyzed.

[0033] Example 4:

[0034] Preparation of Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy: (1) Alloy preparation: according to the target composition Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy, the required pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn, Al-10Sr intermediate alloy raw materials for preparing the target alloy were calculated and weighed respectively; (2) Alloy smelting: the weighed pure aluminum, Al-20Si, Al-10Mn intermediate alloy raw materials are melted in the furnace, the melting temperature is 780℃, after completely melting, the temperature is reduced to 730℃, the pure Mg block wrapped with aluminum foil is added, stirring for 2min, making the composition uniform and standing for 10min, obtaining the required Al-7.5Mg-3.0Si-0.8Mn alloy melt; (3) Adding micro-alloying elements Sr and Bi: Al-10Sr intermediate alloy and Bi metal particles are added to the Al-7.5Mg-3.0Si-0.8Mn alloy melt, after completely melting, stirring for 2min, making the composition uniform, standing for 10min; (4) Melt refining and deslagging: the alloy melt after step (3) is removed from the surface dross, the melt temperature is controlled in the range of 720℃~740℃, the argon blowing method is used to add the deslagging agent, the deslagging agent is mixed and matched by the mass ratio of 1:1 of the commercially available YT-J-1 refining agent and YT-D-4 refining agent, the total addition amount is 1% of the weight of the second melt, standing for 2min; (5) Melt casting forming: the melt temperature in step (4) is controlled at 720℃, then cast into a metal mold preheated to 250℃, obtaining the Sr and Bi compound modification Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy casting, finally sampling and analyzing from the casting.

[0035] Comparative example 1:

[0036] Preparation of Al-6.5Mg-2.5Si-0.7Mn alloy: (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.7Mn alloy, the required pure aluminum, pure magnesium, Al-20Si, Al-10Mn alloy raw materials for preparing the target alloy are calculated and weighed respectively; (2) Alloy smelting: the weighed pure aluminum, Al-20Si, Al-10Mn intermediate alloy raw materials are melted in the furnace, the melting temperature is 780℃, after completely melting, the temperature is reduced to 730℃, the pure Mg block wrapped with aluminum foil is added, stirring for 2min, making the composition uniform and standing for 10min, obtaining the required Al-6.5Mg-2.5Si-0.7Mn alloy melt; (3) Melt refining and deslagging: the alloy melt after step (3) is removed from the surface dross, the melt temperature is controlled in the range of 720℃~740℃, the argon blowing method is used to add the deslagging agent, the deslagging agent is mixed and matched by the mass ratio of 1:1 of the commercially available YT-J-1 refining agent and YT-D-4 refining agent, the total addition amount is 1% of the weight of the second melt, standing for 2min; (4) Melt Casting: The melt temperature in step (3) was controlled at 720 °C, and then cast into a metal mold preheated to 250 °C to obtain an Al-6.5Mg-2.5Si-0.7Mn alloy casting, and finally sample analysis was performed from the casting.

[0037] Comparative Example 2:

[0038] Preparation of Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy: (1) Alloy preparation: According to the target composition Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy, the required pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn, Al-10Sr intermediate alloy raw materials for preparing the target alloy were calculated and weighed respectively; (2) Alloy melting: The weighed pure aluminum, Al-20Si, Al-10Mn intermediate alloy raw materials were melted in the furnace, the melting temperature was 780 °C, after completely melted, the temperature was lowered to 730 °C, the pure Mg block wrapped with aluminum foil was added, stirred for 2 min, and the composition was uniform and kept for 10 min, to obtain the required Al-5.0Mg-2.5Si-0.7Mn alloy melt; (3) Adding micro-alloying elements Sr and Bi: Al-10Sr intermediate alloy and Bi metal particles were added to the Al-5.0Mg-2.5Si-0.7Mn alloy melt, after completely melted, stirred for 2 min, the composition was uniform, and kept for 10 min; (4) Melt refining and slag removal: The alloy melt after melting in step (3) was removed from the surface dross, the melt temperature was controlled in the range of 720 °C~740 °C, the slag remover was added by argon blowing method, the slag remover was mixed and prepared by the mass ratio of 1:1 of commercially available YT-J-1 refining agent and YT-D-4 refining agent, the total addition amount was 1% of the second melt weight, and kept for 2 min; (5) Melt Casting: The melt temperature in step (4) was controlled at 720 °C, and then cast into a metal mold preheated to 250 °C to obtain an Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy casting, and finally sample analysis was performed from the casting.

[0039] Comparative Example 3:

[0040] Preparation of Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy: (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy, the pure aluminum, pure magnesium, Al-20Si, Al-10Mn, Al-10Sr intermediate alloy raw materials required for preparing the target alloy are calculated and weighed respectively; (2) Alloy melting: the weighed pure aluminum, Al-20Si, Al-10Mn intermediate alloy raw materials are melted in the furnace, the melting temperature is 780℃, after completely melting, the temperature is lowered to 730℃, the pure Mg block wrapped with aluminum foil is added, stirring for 2min, making the composition uniform and standing for 10min, obtaining the required Al-6.5Mg-2.5Si-0.7Mn alloy melt; (3) Adding micro-alloying element Sr: adding Al-10Sr intermediate alloy to the Al-6.5Mg-2.5Si-0.7Mn alloy melt, after completely melting, stirring for 2min, making the composition uniform, standing for 10min; (4) Melt refining and slag removal: removing the surface dross of the alloy melt after melting in step (3), controlling the melt temperature in the range of 720℃~740℃, adding the slag remover by argon blowing method, the slag remover is mixed by the mass ratio of 1:1 of commercially available YT-J-1 refining agent and YT-D-4 refining agent, the total addition amount is 1% of the second melt weight, standing for 2min; (5) Melt casting forming: controlling the melt temperature in step (4) to 720℃, then casting into a metal mold preheated to 250℃, obtaining the Sr modified Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy casting, finally sampling and analyzing from the casting.

[0041] Comparative example 4:

[0042] Preparation of Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy: (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy, the pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn intermediate alloy raw materials required for preparing the target alloy are calculated and weighed respectively; (2) Alloy melting: the weighed pure aluminum, Al-20Si, Al-10Mn intermediate alloy raw materials are melted in the furnace, the melting temperature is 780℃, after completely melting, the temperature is lowered to 730℃, the pure Mg block wrapped with aluminum foil is added, stirring for 2min, making the composition uniform and standing for 10min, obtaining the required Al-6.5Mg-2.5Si-0.7Mn alloy melt; (3) Adding micro-alloying element Bi: Bi metal particles are added to the Al-6.5Mg-2.5Si-0.7Mn alloy melt, and after complete melting, stirring is performed for 2 min to make the composition uniform, and it is left to stand for 10 min; (4) Melt refining and slag removal: the alloy melt after melting in step (3) is removed of the surface dross, the melt temperature is controlled in the range of 720-740°C, a slag remover is added by argon blowing method, the slag remover is mixed by commercially available YT-J-1 refiner and YT-D-4 refiner at a mass ratio of 1:1, the total addition amount is 1% of the weight of the second melt, and it is left to stand for 2 min; (5) Melt casting: the melt temperature in step (4) is controlled at 720°C, and then it is cast into a metal mold preheated to 250°C to obtain a Bi-modified Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy casting, and finally samples are taken from the casting for analysis.

[0043] Comparative Example 5:

[0044] Preparation of Al-6.5Mg-2.5Si-0.7Mn-0.1Sr-0.2Bi alloy: (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.7Mn-0.1Sr-0.2Bi alloy, the required pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn, and Al-10Sr intermediate alloy raw materials are calculated and weighed for preparation of the target alloy; (2) Alloy melting: the weighed pure aluminum, Al-20Si, and Al-10Mn intermediate alloy raw materials are melted in the furnace, the melting temperature is 780°C, after complete melting, the temperature is lowered to 730°C, pure Mg blocks wrapped with aluminum foil are added, stirring is performed for 2 min to make the composition uniform, and it is left to stand for 10 min to obtain the required Al-6.5Mg-2.5Si-0.7Mn alloy melt; (3) Adding micro-alloying elements Sr and Bi: Al-10Sr intermediate alloy and Bi metal particles are added to the Al-6.5Mg-2.5Si-0.7Mn alloy melt, and after complete melting, stirring is performed for 2 min to make the composition uniform, and it is left to stand for 10 min; (4) Melt refining and slag removal: the alloy melt after melting in step (3) is removed of the surface dross, the melt temperature is controlled in the range of 720-740°C, a slag remover is added by argon blowing method, the slag remover is mixed by commercially available YT-J-1 refiner and YT-D-4 refiner at a mass ratio of 1:1, the total addition amount is 1% of the weight of the second melt, and it is left to stand for 2 min; (5) Melt Casting: The melt temperature in step (4) is controlled at 720℃, and then cast into a metal mold preheated to 250℃ to obtain a Sr and Bi composite modification Al-6.5Mg-2.5Si-0.7Mn-0.1Sr-0.2Bi alloy casting, and finally sample analysis from the casting.

[0045] Detection:

[0046] According to the method listed in the national standard GB / T 228.1-2021 "Metallic Materials Tensile Test Part 1: Room Temperature Test Method", the alloy castings of Examples 1-4 and Comparative Examples 1-5 are subjected to tensile test, and the specific results are shown in Table 1: Table 1

[0047] and the optical microstructure of the alloy castings of Examples 1-4 and Comparative Examples 1-5 are shown in Figures 1-9 respectively; Among them Figure 5 is the Al-6.5Mg-2.5Si-0.7Mn alloy metallographic microstructure prepared by Comparative Example 1, the alloy is not added with modifier alloy, the morphology of eutectic Mg2Si is lamellar and lath, which seriously cuts the Al matrix and produces stress concentration, forming crack source; Figure 1 is the Al-6.0Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy metallographic microstructure prepared by Example 1; compared with Comparative Example 1 ( Figure 4 ), the morphology of eutectic Mg2Si of the alloy with 0.05Sr and 0.2Bi composite modification is obviously refined and modified from lamellar and lath to fine fibrous and granular; Figure 2 is the Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy metallographic microstructure prepared by Example 2; compared with Comparative Example 1, the morphology of eutectic Mg2Si of the alloy with 0.05Sr and 0.3Bi composite modification is significantly refined and modified from lamellar and lath to fine granular; Figure 3 is the Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy metallographic microstructure prepared by Example 3; compared with Comparative Example 1, the morphology of eutectic Mg2Si of the alloy with 0.05Sr and 0.4Bi composite modification is obviously refined and modified from lamellar and lath to granular; Figure 4The microstructure of Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy prepared in Example 4 is shown in the figure; compared with Comparative Example 1 (Example 2), the eutectic Mg2Si morphology of the alloy with 0.1Sr and 0.4Bi composite modification treatment is obviously modified from lamellar and lath to fine fibrous and granular; Figure 5 The microstructure of Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy prepared in Comparative Example 2 is the same as that in Example 2, and the eutectic Mg2Si morphology of the alloy with 0.05Sr and 0.3Bi composite modification treatment is obviously refined and modified from lamellar and lath to fine granular; Figure 6 The microstructure of Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy prepared in Comparative Example 2 is the same as that in Example 2, and the eutectic Mg2Si morphology of the alloy with 0.05Sr and 0.3Bi composite modification treatment is obviously refined and modified from lamellar and lath to fine granular; Figure 7 The microstructure of Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy prepared in Comparative Example 3 is shown in the figure; compared with Comparative Example 1, the eutectic Mg2Si morphology of the alloy with 0.05Sr modification alone is obviously changed from lamellar and lath to vermicular; Figure 8 The microstructure of Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy prepared in Comparative Example 4 is shown in the figure; compared with Comparative Example 1, the eutectic Mg2Si morphology of the alloy with 0.2Bi modification alone is obviously refined from lamellar and lath to fibrous; Figure 9 The microstructure of Al-6.5Mg-2.5Si-0.7Mn-0.1Sr-0.2Bi alloy prepared in Comparative Example 5 is shown in the figure; compared with Example 2, the eutectic Mg2Si morphology of the alloy with 0.1Sr and 0.2Bi composite modification treatment is only changed from lamellar and lath to fine vermicular; In summary, the alloy prepared in Examples 1-4 has the best performance.

[0048] The above examples are only used to illustrate the technical solutions of the present application, but not limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A cast high-strength and tough Al-Mg alloy, characterized in that: The Al-Mg alloy is composed of the following components in mass percentage: Mg: 6.0% to 7.5%, Si: 2.5% to 3.0%, Mn: 0.6% to 0.8%, Sr: 0.05 to 0.1%, Bi: 0.2 to 0.4%, Fe≤0.2%, and the balance is Al; and the mass ratio of Mg to Si is ≥2.3, and the mass ratio of Bi to Sr is ≥4.

2. A method for preparing the as-cast high-strength and tough Al-Mg alloy according to claim 1, characterized in that: The preparation method comprises the following steps: S1. Pure aluminum, Al-Si master alloy, and Al-Mn master alloy are mixed and completely melted, and then magnesium blocks are added until completely melted, stirred evenly, and allowed to stand to keep warm to obtain a first melt for standby use; S2, adding Al-Sr master alloy and pure Bi to the first melt, stirring evenly after completely melting and standing to maintain heat to complete composite metamorphism, to obtain a second melt for standby use; S3. Refining and deslagging the second melt, and casting to obtain a cast Al-Mg alloy casting.

3. The preparation method according to claim 2, wherein: In the step S1, the Al-Si master alloy is an Al-20Si master alloy, and the Al-Mn master alloy is an Al-10Mn master alloy.

4. The preparation method according to claim 2, wherein: In step S1, the temperature at which the pure aluminum, Al-Si master alloy, and Al-Mn master alloy are completely melted is 770° C. to 800° C.

5. The preparation method according to claim 2, wherein: In step S1, the temperature when adding the magnesium block is controlled to be ≤740° C., and the magnesium block is wrapped with aluminum foil when added, and the stirring time is 2-5 minutes, and the standing and heat preservation time is 10-20 minutes.

6. The preparation method according to claim 2, wherein: In step S2, the Al-Sr master alloy is an Al-10Sr master alloy, and pure Bi is added in the form of metal particles.

7. The preparation method according to claim 2, characterized in that: In step S2, the temperature of the Al-Sr master alloy and pure Bi added to the first melt is ≤740° C., the stirring time is 2-5 minutes, and the standing and heat preservation time is 10-20 minutes.

8. The preparation method according to claim 2, wherein: The specific method of refining and deslagging in step S3 is to add a deslagging agent to the second melt by using an argon blowing method. The deslagging agent is prepared by mixing commercially available YT-J-1 refining agent and YT-D-4 refining agent in a mass ratio of 1:1, and the total addition amount is 1% of the weight of the second melt. After refining and deslagging, the melt is allowed to stand for 2-10 minutes, and the melt temperature is controlled within the range of 720°C-740°C, and then the slag on the surface of the alloy liquid is scraped off.

9. The preparation method according to claim 2, wherein: The casting method in step S3 is to keep the second melt after refining and deslagging at 720° C.-740° C. and cast it into a metal mold preheated at 250° C.-300° C. for molding.

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