JP2018507324A - How to get parts made of low silicon aluminum alloy - Google Patents

Abstract

It relates to parts made of low silicon aluminum alloys including silicon, magnesium, copper, manganese, titanium, and strontium. The part is obtained by a method comprising: casting the alloy into a mold to obtain the part; after casting, releasing the part that still forms the hot preform; Subsequent to cooling the preform, subjecting the preform to an operation suitable for reheating to a temperature in the range of 470 ° C.-550 ° C. and dimensions substantially equal to, but smaller than, the mold cavity dimensions Placing the part between the two shells of the die defining the cavity of the die, and pressing the two shells together strongly to effect the combined action of pressing and surface kneading on the part placed between the shells Stage of effect.

Description

  The present invention relates to the foundry or foundry technical field for producing aluminum parts, in particular in the automotive and aviation fields, and more generally in all kinds of industries.

There are many alloys called “low silicon” alloys. Such alloys have high mechanical properties after T6 heat treatment (Rp _0.2 300 MPa; A% 8%). They are grouped as 6000 (Al-Mg-Si) system in the classification of aluminum alloys. The best known are 6082, 6061, and 6151. Many compositions also exist with the same content as standardized alloys, among which the ones described in EP 0987344 can be mentioned.

  The above-described alloys have been developed to obtain semi-finished products (forging or rolling billets or ingots) designed to deform at high deformation rates (> 50%) during high or low temperature processing. In addition, the geometry of such semi-finished products is simple (bars, rods, or ingots), and thus such alloys with minimized defects by using methods with high solidification rates. Allows to be solidified. Such geometries and such methods result in semi-finished products that are free of defects by using currently familiar techniques. Such defects are, for example, shrinkage holes, cracks, macrosegregation, and macroprecipitation (precipitate formation is very coarse, greater than 100 μm).

European Patent No. 0987344

  Based on the current state of the art, the problem to be solved by the present invention is to make it possible to obtain parts that meet high safety and quality standards and can have complex shapes.

  In order to solve this problem, the present invention provides a method of manufacturing a part made of a 6000 type low silicon aluminum alloy.

A cast microstructure free of manganese and a β-type “needle” precipitate are shown. Single structure and α-type “Chinese script” precipitates from manganese are shown. Fig. 4 shows the removal of Al ₂ Cu copper deposits. Fig. 4 shows the removal of Al ₂ Cu copper deposits. Fig. 4 shows the removal of Al ₂ Cu copper deposits.

More particularly, the present invention relates to silicon in the range of 0.5% -3%, magnesium in the range of 0.65% -1%, in the range of 0.20% -0.40%. Content of copper, content of manganese in the range of 0.15% -0.25%, content of titanium in the range of 0.10% -0.20%, and content in the range of 0 ppm-120 ppm A method of obtaining a part made of a low silicon aluminum alloy containing strontium is provided, the method comprising:
Casting the alloy into a mold to obtain a part;
-After casting, the step of releasing the parts constituting the still hot preform,
Subjecting the preform to an operation suitable for reheating the preform to a temperature in the range of 470 ° C.-550 ° C. after cooling the preform;
Placing said part between two shells of a die defining a cavity of a dimension substantially equal to but smaller than the dimension of the mold cavity;
-Pressing both the two shells together strongly to exert a combined action of pressing and surface kneading on the parts arranged between the shells;
including.

The present invention also provides the following.
・ Implementing the above method in the automotive or aviation field
・ Use the parts obtained by the above method in the automotive field,
Use of alloys in the above method in the aviation field.

  In this method embodiment, after the preform has cooled, the preform is reheated by being placed in a tunnel furnace.

  As a result of these features, the parameters in forging the preform after the casting operation in one step are not the same as in the prior art method with respect to temperature, solidification rate, deformation rate, and forging temperature.

  The claimed alloy satisfies these constraints, especially when the parts must meet safety obligations (suspension system parts are safety parts) and get a satisfactory quality part Make it possible.

Under such constraints, the following can be described as an example.
Unlike the bar or ingot, the preform geometry includes a rough outline of the functional area of the part when it is designed and thus leads to a separated mass of liquid metal or It can have a complex geometric shape that includes part changes. Such separated masses can be “acceptable” by increasing the silicon content (grade AS7G03, standard casting alloy). Due to its reduced content, the alloy becomes more susceptible during solidification, resulting in more shrinkage pore (porosity) defects in number and volume.
The solidification range is a range defined from the liquidus temperature to the eutectic temperature of the target alloy. In the case of a strontium modified AS7G03 type alloy, this range is about 50 ° C. (611 ° C.-562 ° C.). In the case of a low silicon 6000 type alloy, it is about 90 ° C. (655 ° C.-562 ° C.) with macroscopic Mg ₂ Si (or silicon) precipitation as a pseudoeutectic line. The wide solidification range provides a semi-solid region that extends further through the part, so as to reduce defects at the solidification edge, as was done in the past and almost naturally in the AS7G03 alloy. Becomes more difficult.
AS7G03 has little sensitivity to crack formation due to the large amount of eutectic that can fill the cracks that appear during shrinkage during solidification. This is not the case for low silicon alloys with little eutectic, in which case it becomes more sensitive to crack formation and it is necessary to adapt the composition and control the solidification temperature gradient.

  It is also necessary to adjust the chemical composition to obtain a better compromise or tradeoff between casting, forging, and heat treatment parameters and the desired mechanical properties of the finished part. For this purpose, each element of the alloy, its content, and the effect leading to its value are selected and given in detail below.

  The silicon content is in the range of 0.5% -3%. A silicon content of less than 1% results in the highest yield strength and elongation. However, this is the content in which the alloy is most sensitive to crack formation and has the lowest castability or flowability. It is therefore necessary to be able to adapt the silicon content according to the geometry of the part. Complex geometries require a higher content to reduce this sensitivity to crack generation. The maximum content of 3% corresponds to a content beyond which the elongation and yield strength become too low to be still advantageous for producing parts using this type of alloy. To do.

The magnesium content is in the range of 0.65% -1%. This content makes it possible to optimize the density of Mg ₂ Si precipitates in the aluminum matrix. This compensates for the decrease in silicon content, while at the same time being disadvantageous and minimizing macroscopic Mg ₂ Si precipitates that must be dissolved or transformed during the heat treatment. If there are too many precipitates or they are too large, the heat treatment has only a minor effect on their dissolution because the critical dissolution size is exceeded.

The copper content is in the range of 0.20% -0.40%. This content allows Al ₂ Cu precipitates to be formed in the matrix and ensures that macroscopic Al ₂ Cu precipitates are completely absent. Due to the absence of such macroscopic precipitates, a high forging temperature can be maintained, thereby minimizing the forging force (forging in a single step). The main precipitates formed in the presence of copper are Al ₂ Cu and AlMgSiCu, which melt at 490 ° C. and 525 ° C., respectively, and these presences prevent forging at high temperatures and cause the alloy to burn Eliminate the risk that parts will become unusable. Such deterioration can be compared to the destruction of the alloy. Higher copper content also increases the alloy's sensitivity to crack formation. This is because the eutectic to be solidified remains at a low temperature (490 ° C. or 525 ° C.) where the mechanical stress exerted on the part (related to shrinkage during solidification) is large.

  The manganese content is in the range of 0.15% to 0.25%. This content avoids the formation of AlFeSi precipitates in β-type (very harmful platelet form), but rather allows the formation of α-type AlFeMnSi precipitates (less harmful) Chinese script form). This makes it possible to maximize the elongation of the final product obtained by the cover pressing method. This effect is most often used when the amount of manganese and iron is high because manganese and iron not only result in high hardening of the alloy, but also produce larger precipitates during solidification. Such large precipitates are detrimental to proper elongation. However, the alloys of the present invention, as shown, are designed for a cover press process that is forged in a single step and does not involve the large deformations normally encountered in forging, rolling or extrusion. Such large deformation makes it possible to fragment large deposits and make them harmless while also maintaining the effect of curing. In the alloy of the present invention, the influence of iron-based precipitates on the mechanical properties should be minimized during the casting stage. This is because single-step forging does not deform the parts to the extent that they are sufficient to change the morphology, so their morphology is no longer altered. Finally, this manganese content is compatible with the cooling rate obtained when casting in permanent molds, and facilitates the formation of α-type AlFeMnSi precipitates for this rate.

  The titanium content is in the range of 0.10% -0.20%. Its content is necessary to obtain a fine particle size that has a great influence on the effective production of particles and the mechanical properties of these alloys.

  The content of strontium is in the range of 0 ppm to 120 ppm. This content is necessary to have a small amount of eutectic fibrous solidification formed. This occurs mainly with silicon contents exceeding 1.5%.

  It can be seen that the composition of this alloy is adapted to provide solidification that allows the mechanical properties to be maximized despite the low level of deformation that occurs during the cover pressing process.

  However, solidification defects, such as grain boundary shrinkage hole solidification defects at grain boundaries, have a branching and diffused morphology that weakens the casting, ie, the part obtained by casting.

  The edge press forging operation makes it possible to reclose and recombine such defects while controlling the deformation rate at the design stage. The temperature / deformation pair can eliminate the defect. The table below shows the mechanical properties of castings and parts using the cover press method after T6 heat treatment of low silicon alloys. It can be noted that the ultimate tensile strength Rm and the ultimate elongation are improved.

Finally, this composition makes it possible to reduce the usual heat treatment complexity of Al-Mg-Si-Cu type alloys. Silicon content, solidification rate, and grain refinement result in macroscopic Mg ₂ Si precipitates with dimensions and morphology that facilitate dissolution during heat treatment.

  To illustrate the importance of manganese content and copper content, reference is made to the figures in the accompanying drawings showing the metallographic structure of the part. FIG. 1 shows a cast microstructure without manganese and β-type “needle” precipitates, and FIG. 2 shows a single structure and α-type “Chinese script” precipitates with manganese.

3, 4 and 5 show the removal of Al ₂ Cu copper deposits.

3 and 4, the copper content is greater than 0.40%, which results in the presence of Al ₂ Cu precipitates. FIG. 4 shows an example in which deposits of AlFeMnSi and Mg ₂ Si surrounded by Al ₂ Cu precipitates can be observed.

Figure 5 shows that _{the Al} 2 Cu precipitates are not present, shows a copper content in the range of 0.20% -0.40% in accordance with the present invention.

Claims (3)

A method of obtaining a part made of a low silicon aluminum alloy comprising:
The alloy is
A silicon content in the range of 0.5% -3%;
A magnesium content in the range of 0.65% -1%;
A copper content in the range of 0.20% -0.40%;
A manganese content in the range of 0.15% -0.25%;
Titanium with a content in the range of 0.10% -0.20%; and strontium with a content in the range of 0 ppm-120 ppm;
Including
The method
Casting the alloy into a mold to obtain a part;
-After casting, the step of releasing the parts constituting the still hot preform,
Subjecting the preform to an operation suitable for reheating the preform to a temperature in the range of 470 ° C.-550 ° C. after cooling the preform;
Placing said part between two shells of a die defining a cavity of a dimension substantially equal to but smaller than the dimension of the mold cavity;
-Pressing both the two shells together strongly to exert a combined action of pressing and surface kneading on the parts arranged between the shells;
Including a method.   Use of a part obtained by the method according to claim 1 in the automotive field.   Use of an alloy in the method according to claim 1 in the aviation field.

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