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

Abstract

The application provides a cast high-strength and high-toughness Al-Mg alloy and a preparation method thereof, and relates to the field of cast aluminum alloys.The cast high-strength and high-toughness Al-Mg alloy is composed of the following 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: less than or equal to 0.2%, and the balance of Al; and 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.The application overcomes the defects of the prior art, and significantly improves the strength and plasticity of the Al-Mg alloy in the cast state, so as to meet the application of the Al-Mg alloy in the fields of automobiles, communications, electronics or aerospace.

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 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 easy to absorb and gather in front of the growth interface of the first precipitated eutectic phase during the eutectic reaction of Al-Mg2Si, and the modification of the eutectic phase, but the tensile strength after modification in the gravity casting state is only 230MPa~250MPa, and the elongation is 6%~10%.

[0005] In the above method, the addition of Si element in 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, but 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 becomes the current research hotspot. 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:

[0008] 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.

[0009] The preparation method of the cast high strength and toughness Al-Mg alloy comprises the following steps:

[0010] S1, pure aluminum, Al-Si intermediate alloy, Al-Mn intermediate alloy are mixed, melted completely, then magnesium block is added to melt completely, stirred uniformly and placed for heat preservation, to obtain a first melt for standby;

[0011] S2, Al-Sr intermediate alloy, pure Bi are added to the first melt, stirred uniformly after complete melting and placed for heat preservation to complete composite modification, to obtain a second melt for standby;

[0012] S3, the second melt is refined and slag is removed, and is cast into shape to obtain as-cast Al-Mg alloy castings.

[0013] Preferably, in the step S1, the Al-Si intermediate alloy is Al-20Si intermediate alloy, and the Al-Mn intermediate alloy is Al-10Mn intermediate alloy.

[0014] Preferably, in the step S1, the temperature for mixing, melting completely of pure aluminum, Al-Si intermediate alloy and Al-Mn intermediate alloy is 770-800℃.

[0015] Preferably, in the step S1, the temperature for adding magnesium block is controlled to be ≤740℃, the magnesium block is wrapped with aluminum foil when added, the stirring time is 2-5min, and the time for placing for heat preservation is 10-20min.

[0016] Preferably, in the step S2, the Al-Sr intermediate alloy is Al-10Sr intermediate alloy, and the pure Bi is added in the form of metal particles.

[0017] Preferably, in the step S2, the temperature for adding Al-Sr intermediate alloy and pure Bi to the first melt is ≤740℃, the stirring time is 2-5min, and the time for placing for heat preservation is 10-20min.

[0018] Preferably, in the step S3, the specific method for refining and removing slag is to add slag removing agent to the second melt by argon blowing method, the slag removing agent is mixed and matched from commercially available YT-J-1 refining agent and YT-D-4 refining agent at a mass ratio of 1:1, the total addition amount is 1% of the weight of the second melt, after refining and removing slag, the melt is placed for 2-10min, the melt temperature is controlled in the range of 720-740℃, and then the surface scum of the alloy liquid is cleaned.

[0019] Preferably, in the step S3, the method for casting and forming is to keep the second melt after refining and removing slag at 720-740℃, and then cast into a metal mold preheated to 250-300℃ for forming.

[0020] The preparation principle is as follows:

[0021] 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 element 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%.

[0022] 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.

[0023] 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.

[0024] Compound modification:

[0025] 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 should not be excessive, and the refining effect will decrease 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 eutectic Mg2Si changes from a platelet structure to 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, the eutectic Mg2Si is formed in the form of fine particles, and the strength and plasticity of the alloy in the as-cast state are greatly improved.

[0026] The application provides an as-cast high-strength and high-toughness Al-Mg alloy and a preparation method thereof.

[0027] (1) The cast high strength and toughness Al-Mg alloy prepared in the application has high strength in cast state, which is mainly from the second phase strengthening effect of Mg2Si formed by adding Si and Mg and the solid solution strengthening effect of residual Mg and a small amount of Mn in Al matrix.

[0028] (2) The coarse lamellar eutectic Mg2Si phase in the cast high strength and toughness Al-Mg alloy is refined and modified by adding elements Sr and Bi micro-alloying, which significantly improves the modification and refinement effect of eutectic Mg2Si, and finally forms fine granular eutectic Mg2Si, and by limiting the mass ratio of Mg and Si≥2.3, the strength and plasticity of the alloy in cast state are greatly improved, and the performance of the final alloy is comprehensively improved.

[0029] (3) The cast aluminum alloy prepared in the application has high strength and high plasticity in cast state without heat treatment, and the tensile strength is more than 311 MPa and the elongation reaches 22%.

[0030] (4) The cast aluminum alloy prepared in the 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

[0031] Figure 1 It is the optical microstructure diagram of Al-6.0Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy in Example 1;

[0032] Figure 2 It is the optical microstructure diagram of Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy in Example 2;

[0033] Figure 3 It is the optical microstructure diagram of Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy in Example 3;

[0034] Figure 4 It is the optical microstructure diagram of Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy in Example 4;

[0035] Figure 5 It is the optical microstructure diagram of Al-6.5Mg-2.5Si-0.7Mn alloy in Comparative Example 1;

[0036] Figure 6 It is the optical microstructure diagram of Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy in Comparative Example 2;

[0037] Figure 7 Optical microstructure chart of the Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy in Comparative Example 3;

[0038] Figure 8 Optical microstructure chart of the Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy in Comparative Example 4.

[0039] Figure 9 Optical microstructure chart of the Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.1Bi alloy in Comparative Example 5. DETAILED DESCRIPTION

[0040] 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 but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0041] Embodiment 1:

[0042] 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:

[0043] Pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, Al-10Mn, Al-10Sr intermediate alloy were used as raw materials for batching, and the Al-6.5Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy melt was prepared by melting, and finally cast into shape. The specific steps and process parameters are as follows:

[0044] (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi 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;

[0045] (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, so that the composition was uniform and placed for 10min, and the required Al-6.5Mg-2.5Si-0.6Mn alloy melt was obtained;

[0046] (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-0.6Mn alloy melt, and after complete melting, stirring is carried out for 2 min to make the composition uniform, and standing and heat preservation is carried out for 10 min;

[0047] (4) Melt refining and deslagging: the alloy melt after melting in step (3) is removed from the surface dross, the melt temperature is controlled in the range of 720℃~740℃, the deslagging agent is added by argon blowing method, the deslagging agent is mixed and prepared by mixing the commercially available YT-J-1 refining agent and YT-D-4 refining agent in a mass ratio of 1:1, the total addition amount is 1% of the weight of the second melt, and standing and heat preservation is carried out for 2 min;

[0048] (5) Melt casting forming: 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 treated Al-6.5Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy casting, and finally sample analysis is carried out from the casting.

[0049] Example 2:

[0050] Preparation of Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy:

[0051] (1) Alloy preparation: according to the target composition Al-6.5Mg-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 are calculated and weighed;

[0052] (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 complete melting, the temperature is lowered to 730℃, the pure Mg block wrapped with aluminum foil is added, stirring is carried out for 2 min to make the composition uniform, and standing and heat preservation is carried out for 10 min to obtain the required Al-6.5Mg-2.5Si-0.7Mn alloy melt;

[0053] (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 carried out for 2 min to make the composition uniform, and standing and heat preservation is carried out for 10 min;

[0054] (4) Melt refining and slag removal: remove the dross on the surface of the melt after melting in 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 commercially available YT-J-1 refining agent and YT-D-4 refining agent with a 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;

[0055] (5) Melt casting: control the melt temperature in step (4) at 720°C, then cast into a metal mold preheated to 250°C to obtain a Sr and Bi composite modification treated Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy casting, and finally analyze the sample from the casting.

[0056] Example 3:

[0057] Preparation of Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy:

[0058] (1) Alloy preparation: according to the target composition Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi 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;

[0059] (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 for 10 min, obtain the required Al-7.0Mg-3.0Si-0.7Mn alloy melt;

[0060] (3) Add micro-alloying elements Sr and Bi: add Al-10Sr intermediate alloy and Bi metal particles to the Al-7.0Mg-3.0Si-0.7Mn alloy melt, after complete melting, stir for 2 min, make the composition uniform, and stand for 10 min;

[0061] (4) Melt refining and slag removal: remove the dross on the surface of the melt after melting in 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 commercially available YT-J-1 refining agent and YT-D-4 refining agent with a 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;

[0062] (5) Melt casting forming: the melt temperature in step (4) is controlled at 720℃, then cast into a metal mold preheated to 250℃, to obtain Sr and Bi composite modification of Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy castings, finally sample analysis from the castings.

[0063] Example 4:

[0064] Preparation of Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy:

[0065] (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 are calculated and weighed respectively;

[0066] (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 melting, 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-7.5Mg-3.0Si-0.8Mn alloy melt;

[0067] (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 melting, stirring for 2min, the composition is uniform, and placed for 10min;

[0068] (4) Melt refining and slag removal: the surface dross of the alloy melt after melting in step (3) is removed, the melt temperature is controlled in the range of 720℃~740℃, the deslagging agent is added by argon blowing method, the deslagging agent 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, and the temperature is kept for 2min;

[0069] (5) Melt casting forming: the melt temperature in step (4) is controlled at 720℃, then cast into a metal mold preheated to 250℃, to obtain Sr and Bi composite modification of Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy castings, finally sample analysis from the castings.

[0070] Comparative Example 1:

[0071] Preparation of Al-6.5Mg-2.5Si-0.7Mn alloy:

[0072] (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;

[0073] (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;

[0074] (3) Melt refining and deslagging: the alloy melt after melting in step (3) is removed from the surface dross, the melt temperature is controlled in the range of 720℃~740℃, the deslagging agent is added by argon blowing method, the deslagging agent is 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 is 1% of the second melt weight, standing for 2min;

[0075] (4) Melt casting forming: the melt temperature in step (3) is controlled at 720℃, then cast into a metal mold preheated to 250℃, obtaining Al-6.5Mg-2.5Si-0.7Mn alloy castings, finally sampling and analyzing from the castings.

[0076] Comparative Example 2:

[0077] Preparation of Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy:

[0078] (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 are calculated and weighed respectively;

[0079] (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-5.0Mg-2.5Si-0.7Mn alloy melt;

[0080] (3) Adding micro-alloying elements Sr and Bi: Al-10Sr master alloy and Bi metal particles were added into the Al-5.0Mg-2.5Si-0.7Mn alloy melt, and after complete melting, stirring was carried out for 2 min to make the composition uniform, and then the melt was kept for 10 min;

[0081] (4) Melt refining and slag removal: the alloy melt after melting in step (3) was subjected to slag removal on the surface of the melt, the melt temperature was controlled in the range of 720-740°C, argon blowing method was used to add slag removal agent, the slag removal agent was mixed and prepared from commercially available YT-J-1 refining agent and YT-D-4 refining agent at a mass ratio of 1:1, the total addition amount was 1% of the weight of the second melt, and the melt was kept for 2 min;

[0082] (5) Melt casting: the melt in step (4) was controlled at a temperature of 720°C, and then cast into a metal mold preheated to 250°C to obtain a Sr and Bi composite modification treated Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy casting, and finally the casting was sampled and analyzed.

[0083] Comparative Example 3:

[0084] Preparation of Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy:

[0085] (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy, the required pure aluminum, pure magnesium, Al-20Si, Al-10Mn, and Al-10Sr master alloy raw materials were calculated and weighed for preparing the target alloy;

[0086] (2) Alloy melting: the weighed pure aluminum, Al-20Si, and Al-10Mn master alloy raw materials were melted in the furnace, the melting temperature was 780°C, after complete melting, the temperature was lowered to 730°C, pure Mg blocks wrapped with aluminum foil were added, stirring was carried out for 2 min to make the composition uniform, and the melt was kept for 10 min, obtaining the required Al-6.5Mg-2.5Si-0.7Mn alloy melt;

[0087] (3) Adding micro-alloying element Sr: Al-10Sr master alloy was added into the Al-6.5Mg-2.5Si-0.7Mn alloy melt, after complete melting, stirring was carried out for 2 min to make the composition uniform, and the melt was kept for 10 min;

[0088] (4) Melt refining and slag removal: the floating slag on the surface of the alloy melt after melting in step (3) is removed, the melt temperature is controlled in the range of 720-740 °C, the slag remover is added by argon blowing method, the slag remover is mixed and prepared by commercially available YT-J-1 refining agent and YT-D-4 refining agent with a mass ratio of 1:1, the total addition amount is 1% of the weight of the second melt, and the melt is kept for 2 min;

[0089] (5) Melt casting: the melt temperature in step (4) is controlled at 720 °C, and then cast into a metal mold preheated to 250 °C to obtain a Sr-modified Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy casting, and finally the casting is sampled and analyzed.

[0090] Comparative Example 4:

[0091] Preparation of Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy:

[0092] (1) Alloy preparation: according to the target composition Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy, the required pure aluminum, pure magnesium, pure Bi metal particles, Al-20Si, and Al-10Mn intermediate alloy raw materials are calculated and weighed for preparing the target alloy;

[0093] (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, the pure Mg block wrapped with aluminum foil is added, and stirred for 2 min to make the composition uniform and kept for 10 min, obtaining the required Al-6.5Mg-2.5Si-0.7Mn alloy melt;

[0094] (3) Adding micro-alloying element Bi: Bi metal particles are added to the Al-6.5Mg-2.5Si-0.7Mn alloy melt, after complete melting, stirring for 2 min to make the composition uniform, and keeping for 10 min;

[0095] (4) Melt refining and slag removal: the floating slag on the surface of the alloy melt after melting in step (3) is removed, the melt temperature is controlled in the range of 720-740 °C, the slag remover is added by argon blowing method, the slag remover is mixed and prepared by commercially available YT-J-1 refining agent and YT-D-4 refining agent with a mass ratio of 1:1, the total addition amount is 1% of the weight of the second melt, and the melt is kept for 2 min;

[0096] (5) Melt casting forming: the melt temperature in step (4) is controlled at 720℃, then cast into a metal mold preheated to 250℃, to obtain a Bi modified Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy casting, and finally sample analysis from the casting.

[0097] Comparative Example 5:

[0098] Preparation of Al-6.5Mg-2.5Si-0.7Mn-0.1Sr-0.2Bi alloy:

[0099] (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, Al-10Sr intermediate alloy raw materials for preparing the target alloy are calculated and weighed respectively;

[0100] (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, to make the composition uniform and stand for 10min, to obtain the required Al-6.5Mg-2.5Si-0.7Mn alloy melt;

[0101] (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, after completely melted, stirred for 2min, to make the composition uniform, stand for 10min;

[0102] (4) Melt refining and slag removal: the alloy melt after melting in step (3) is removed from the surface dross, the melt temperature is controlled in the range of 720℃~740℃, the deslagging agent is added by argon blowing method, the deslagging agent is 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 is 1% of the second melt weight, stand for 2min.

[0103] (5) Melt casting forming: the melt temperature in step (4) is controlled at 720℃, then cast into a metal mold preheated to 250℃, to obtain a Bi modified Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy casting, and finally sample analysis from the casting.

[0104] Detection:

[0105] According to the method listed in the national standard GB / T 228.1-2021 “Metallic materials-tensile testing-Part 1: Method of test at room temperature”, 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 below:

[0106] Table 1

[0107]

[0108] The optical microstructure diagrams of the alloy castings of Examples 1-4 and Comparative Examples 1-5 are shown in Figures 1-5, respectively. Figures 1-9

[0109] In which Figure 5 is the metallographic microstructure of the Al-6.5Mg-2.5Si-0.7Mn alloy prepared in Comparative Example 1, the alloy is not added with a modifier alloy, and the morphology of the eutectic Mg2Si is lamellar and lath-shaped, which seriously divides the Al matrix and produces stress concentration to form a crack source;

[0110] Figure 1 is the metallographic microstructure diagram of the Al-6.0Mg-2.5Si-0.6Mn-0.05Sr-0.2Bi alloy prepared in Example 1; compared with Comparative Example 1 ( Figure 4 ), the morphology of the eutectic Mg2Si of the alloy treated by adding 0.05Sr and 0.2Bi composite modification is obviously refined and modified from lamellar and lath-shaped to fine fibrous and granular;

[0111] Figure 2 is the metallographic microstructure diagram of the Al-6.5Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy prepared in Example 2; compared with Comparative Example 1, the morphology of the eutectic Mg2Si of the alloy treated by adding 0.05Sr and 0.3Bi composite modification is significantly refined and modified from lamellar and lath-shaped to fine granular;

[0112] Figure 3 is the metallographic microstructure diagram of the Al-7.0Mg-3.0Si-0.7Mn-0.05Sr-0.4Bi alloy prepared in Example 3; compared with Comparative Example 1, the morphology of the eutectic Mg2Si of the alloy treated by adding 0.05Sr and 0.4Bi composite modification is obviously refined and modified from lamellar and lath-shaped to granular;

[0113] Figure 4 is the metallographic microstructure diagram of the Al-7.5Mg-3.0Si-0.8Mn-0.1Sr-0.4Bi alloy prepared in Example 4; compared with Comparative Example 1 ( Figure 5 ​), the morphology of eutectic Mg2Si of the alloy with 0.1 Sr and 0.4 Bi composite modification treatment is obviously modified from lamellar and lath to fine fibrous and granular;

[0114] Figure 6 The metallographic microstructure of the Al-5.0Mg-2.5Si-0.7Mn-0.05Sr-0.3Bi alloy prepared for Comparative Example 2 is the same as that of Example 2, and the morphology of eutectic Mg2Si of the alloy with 0.05 Sr and 0.3 Bi composite modification treatment is obviously modified from lamellar and lath to fine granular;

[0115] Figure 7 The metallographic microstructure of the Al-6.5Mg-2.5Si-0.7Mn-0.05Sr alloy prepared for Comparative Example 3 is shown in the schematic diagram, and compared with Comparative Example 1, the morphology of eutectic Mg2Si of the alloy with 0.05 Sr modification alone is obviously changed from lamellar and lath to vermicular;

[0116] Figure 8 The metallographic microstructure of the Al-6.5Mg-2.5Si-0.7Mn-0.2Bi alloy prepared for Comparative Example 4 is shown in the schematic diagram, and compared with Comparative Example 1, the morphology of eutectic Mg2Si of the alloy with 0.2 Bi modification alone is obviously modified from lamellar and lath to fibrous;

[0117] Figure 9 The metallographic microstructure of the Al-6.5Mg-2.5Si-0.7Mn-0.1Sr-0.2Bi alloy prepared for Comparative Example 5 is shown in the schematic diagram, and compared with Example 2, the morphology of eutectic Mg2Si of the alloy with 0.1 Sr and 0.2 Bi composite modification treatment is only changed from lamellar and lath to fine vermicular;

[0118] In summary, the alloy prepared in Examples 1-4 has the best performance.

[0119] The above examples are only used to illustrate the technical solutions of the present application, but not limit the same; 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. An as-cast high strength-to-toughness Al-Mg alloy, characterized by, 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 of Al; and the mass ratio of Mg to Si is ≥2.3, and the mass ratio of Bi to Sr is ≥4; The preparation method of the as-cast high-strength and high-toughness Al-Mg alloy comprises the following steps: S1, completely melt the pure aluminum, Al-Si intermediate alloy and Al-Mn intermediate alloy, then add magnesium blocks to completely melt, uniformly stir and stand for heat preservation to obtain a first melt for standby; S2, add Al-Sr intermediate alloy and pure Bi to the first melt, completely melt, uniformly stir and stand for heat preservation to complete the composite modification to obtain a second melt for standby; S3, refine and remove slag from the second melt, and cast to form an as-cast Al-Mg alloy casting.

2. The alloy of claim 1 wherein: In the step S1, the Al-Si intermediate alloy is Al-20Si intermediate alloy, and the Al-Mn intermediate alloy is Al-10Mn intermediate alloy.

3. The alloy of claim 1 wherein: In the step S1, the temperature for completely melting the pure aluminum, Al-Si intermediate alloy and Al-Mn intermediate alloy is 770-800°C.

4. The alloy of claim 1 wherein: In the step S1, the temperature for adding the magnesium blocks is controlled to be ≤740°C, the magnesium blocks are wrapped with aluminum foil when added, the stirring time is 2-5 min, and the standing time for heat preservation is 10-20 min.

5. The alloy of claim 1 wherein: In the step S2, the Al-Sr intermediate alloy is Al-10Sr intermediate alloy, and the pure Bi is added in the form of metal particles.

6. The alloy of claim 1 wherein: In the step S2, the temperature for adding the Al-Sr intermediate alloy and pure Bi to the first melt is ≤740°C, the stirring time is 2-5 min, and the standing time for heat preservation is 10-20 min.

7. The alloy of claim 1 wherein: In the step S3, the specific method for refining and removing slag is to add a slag removal agent to the second melt by argon blowing method, the slag removal agent is mixed by a 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 weight of the second melt, and after refining and removing slag, the melt is stood for 2-10 min, the melt temperature is controlled to be in the range of 720-740°C, and then the surface scum of the alloy liquid is cleaned.

8. The alloy of claim 1 wherein: In the step S3, the method for casting and forming is to maintain the second melt after refining and removing slag at 720-740°C, and then cast into a preheated metal mold at 250-300°C to form.

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