Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
  • C22C21/04—Modified aluminium-silicon alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/043—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with silicon as the next major constituent

Definitions

• the invention relates to a method for improving the mechanical properties of aluminum-silicon alloys. Specifically stated, the invention relates to a heat treatment process for improving the material ductility of objects consisting of a preferably refined or refined aluminum-silicon, optionally containing a further alloy and / or contaminant casting or wrought alloy with a eutectic phase component, which objects are subjected to an annealing treatment with subsequent aging.
• the invention relates to an object made of preferably at least one refinement element, optionally containing magnesium and further alloy and / or impurity elements containing aluminum-silicon alloy with a eutectic phase component consisting essentially of an ⁇ X-Al matrix and silicon precipitates.
• Aluminum forms a simple eutectic system with silicon, the eutectic point being at a Si concentration of 12.5% by weight and a temperature of 577 ° C.
• the material properties on the one hand, but on the other hand also the costs or the economic conditions of the production are important, because longer annealing treatments at higher temperatures as well as necessary message processes caused by the so-called gravitational creeping may be necessary in the case of long-term annealing.
• an Al-Si alloy in state F mostly has low material strength values R p and relatively high elongation at break A.
• Solution heat treatments at high temperatures with a long duration have the disadvantage of, as mentioned earlier, gravitational creeping of the part and a complex temperature-time treatment process. For economic reasons, it is therefore often avoided to achieve the highest strength and good ductility of the material with T6, and a treatment state T5 is selected for the object. The significantly lower material strength due to T5 may have to be compensated for by design changes to the component.
• the invention now aims to provide a new economical method of heat treatment, with which the ductility of the material can be increased significantly without large drops in material strength compared to T6 or a significantly higher ductility and higher material strength compared to T5 is reached.
• the objective of the process is achieved in that the solution heat treatment as an impact heat treatment consisting of rapid heating to an annealing temperature of 400 ° C.-555 ° C., holding at this temperature with a holding time of at most 14.8 minutes and a subsequent forced cooling is carried out essentially at room temperature.
• the advantages achieved with the invention are essentially to be seen in the fact that the highest ductility values of the material can be achieved with a simple high-temperature, short-time annealing. Furthermore, a so-called impact annealing causes little or no component warping or warping of the object, so that it may also not be necessary to straighten it.
• the short-term annealing treatment is also highly economical and can be easily integrated into a manufacturing sequence, for example by means of a continuous furnace, an adjustment of the material strength can then mostly be done using a coordinated technology for arrnaiis storage.
• the shock annealing treatment is carried out with a holding time of less than 6.8 minutes, preferably with a time period of 1.7 to possibly at most 5 minutes, the majority of the Al-Si alloys are greatest increases in ductility.
• the article is warmed up after the annealing, it is advantageous to fix it at a temperature in the range between 150 ° C and 200 ° C for a period of 1 to 14 hours.
• the article, following the impact annealing is cold-aged at substantially room temperature.
• the further object of the invention is achieved in that the silicon precipitates are spheroidized in the eutectic phase portion and have an average cut area, Asi, of less than 4 ⁇ m.
• the advantages of such a microstructure can essentially be seen in the fact that crack initiation in the material is substantially reduced by the spheroidization of the Si precipitates and their fineness, and the material ductility is improved.
• the spheroidization and the small size provide a favorable morphology of the brittle eutectic silicon and lead to significantly higher elongation at break values of the material.
• the stress peaks at the phase interface Si-Al are reduced under mechanical load.
• a transcrystalline fracture of the material was also found in tests, which indicates its highest ductility.
• it can be advantageous if the silicon deposits in the eutectic phase portion are spheroidized and have an average cutting area of less than 2 ⁇ m 2 .
• the inventive solution is achieved in that the mean free path between the silicon particles, ⁇ Sj , in the eutectic phase component, defined as the root of a square measuring area divided by the number of silicon particles contained in it has a size of less than 4 ⁇ m, preferably less than 3 ⁇ m, in particular less than 2 ⁇ m, a particularly homogeneous stress distribution is achieved with the lowest stress peak values in the loaded material, because the distance between the small-area silicon particles essentially depends on the flow behavior of the Material affects in a corresponding stress state.
• the determination of the mean distance between the Si particles, ⁇ si is again shown formally below.
• AQua rat square reference area in ⁇ m 2
• N silicon number of Si particles
• n number of images measured
• a solution annealing according to the prior art which is provided as a long-term annealing with 2 to 12 hours for a diffusion of the alloy components effective for hardening and their enrichment in the mixed crystal, also brings about a spheroidization of the silicon particles as a side effect, but these particles are due to the long Annealing time very large and roughly distributed, which can have an adverse effect on the fracture behavior of the material. It was quite surprising that a eutectic silicon network can be spheroidized invention by a brief shock annealing even in small periods of a few minutes to give a favorable micro S compture of the material is achievable.
• the temperature for the shock annealing is as high as possible, but below the lowest melting phase, preferably 5 to 20 ° C below.
• the silicon particles are subjected to diffusion-controlled growth with increasing glow time, whereby the initially favorable high spheroidization density, ⁇ si, decreases.
• ⁇ si defined as the number of spheroidized eutectic silicon particles per 100 ⁇ m 2 has a value greater than 10, but preferably 20 ,
• ⁇ si average spheroidization density of the eutectic Si particles
• the work has shown that essentially any of the Al-Si alloys containing eutectic can be provided with a structure according to the invention and that the objects formed therefrom have high ductility values of the material. Increasing the quality and improving the elongation at break are particularly efficient if the article is produced using the thixocasting process.
• Fig. 1 Bar graph Mechanical material values depending on the heat treatment condition
• Fig. 1 the R p o ⁇ yield strength values and the elongation at break values A of samples from a test component made of an alloy AlSi7MgO, 3, which part was produced in the thixocasting process, are shown in a bar graph:
• the values of the heat treatment state T6 (12 hours 540 ° C + 4 hours 160 ° C) of the material are compared to those using the method T6x according to the invention after an impact glow time of 1 minute (T6xl), after 3 minutes (T6x3) and after 5 minutes (T6x5) at a temperature of 540 ° C have been achieved. All samples were aged for 4 hours at a temperature of 160 ° C.
• Results of the tensile tests show that the samples have a significantly higher elongation at break after an impact heat treatment, the state T6x3 causing an increase in A of around 60% compared to T6.
• the state values F, T4x3, T5, T6x3 and T6 are again compared with respect to the R p o_ 2 and the elongation at break A in bar form. Striking increases in elongation at break values are considered comparatively 'turn given.
• the material can be aged cold (T4x3) or warm (T6x3) after an impact anneal with 3 minutes in order to obtain superior elongation at break properties according to the invention.
• 3 and 4 show scanning electron microscopes - images of Si precipitates.
• suitable binary images In order to be able to evaluate the micrographs quantitatively, suitable binary images must be available. Up to a glow time of 2 hours inclusive, the images were taken with the scanning electron microscope after the sections had been etched for 30 seconds with a solution of ⁇ 9.5% water and 0.5% hydrofluoric acid. After 4 hours of annealing, the sections were etched with the cellar solution and the images could be taken with the light microscope. All the images were then digitally post-processed with the Adobe Photoshop 5.0 program and evaluated with the Leica QWin V2.2 image analysis program, the minimum detection area being 0.1 ⁇ m 2 .
• FIG. 3 shows the material AlSi7MgO, 3 after a usual T6 annealing time of 12 hours by means of an SEM image.
• 4 is the Microstructure of the same material according to a Stoßguart-se -a ⁇ aitfflg "by _. IviTnuten reproduced. A spheroidization of the silicon precipitates is clearly visible after a short time (Fig. 4) and the diffusion-controlled growth thereof after long annealing times (Fig. 3).
• FIG. 5 and FIG. 6 show the average sectional area A S J of the silicon particles during the grinding test as a function of the annealing time at 540 ° C. 4 with logarithmic time axis, the increase in the average sectional area of the Si particles, which characterizes the particle size, can be clearly seen. 6 shows the increase in the average silicon areas within the first 60 minutes due to diffusion.
• the mean size of the silicon particles which increases with the annealing time, depends to a large extent on the initial size of the Si particles in the eutectic. Since in the case mentioned there is an extremely well refined and finely distributed silicon, the time in which a critical mean silicon area, Asi, of approx ,
• the drop in the mean spheroidization density, ⁇ si, as a function of the glow time is shown in FIG. 8.
• the steep drop in the mean spheroidization density begins at 1.7 minutes and leads to a pronounced loss of ductility from a value of ⁇ si ⁇ 10. At higher annealing temperatures, this value can be reached after 14 to 25 minutes, whereby a density value of greater than 20 must be provided for superior elongation at break values.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Investigating And Analyzing Materials By Characteristic Methods (AREA)
• Conductive Materials (AREA)
• Silicon Compounds (AREA)
• Heat Treatment Of Articles (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Powder Metallurgy (AREA)
• Laminated Bodies (AREA)
• Ceramic Products (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)

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