DE1558772C - Process for the production of cast bodies made of aluminum or aluminum alloys with improved fatigue strength - Google Patents

Description

3 4

mechanically rather high pressures are used. that the largest dimension does not exceed this value - For example, pressures from 14.0 to 35.0 kp / mm ^{2 can} exceed. It has been found that at substantially or even much higher pressures up to 70 kgf / mm ² or removal of the micropores in the order of magnitude more using conventional presses, from 2.54 to 25.4 μ. the fatigue strength of aluminum. 5 miniumgußmassen is significantly increased. Inventive

Since the isostatic pressures can be easily improved by applying the casting compounds, their internal structure The application of isostatic pressure, such as beDauer the exercise often be relatively short, wrote, goes back, are essentially free of ' z. B. 15 seconds, or in some cases even micropores with a size greater than 2.54 μ, with the inner less, although it is otherwise essentially that of a cast to ensure a consistently good structure For results it is advisable to hold the pressure for 15 seconds. is, and show a markedly improved fatigue or more exercise. 'strength of 25 percent or more. It is

When isostatic flow pressure is used, it can be assumed that the improvement in the fatigue casting compound is placed in a chamber; strength is due to the elimination of the microporosity, as described by the desired isostatic pressure 15; accordingly, the appropriate pressure level should have been brought up, duration during which the temperature and the iso while the casting compound is maintained at a static pressure as provided herein, sufficient temperature is maintained. Due to the current economic efficiency, in order to make the casting compound essentially free of national limits, the autoclaves or the like are to be made of microporosity-like properties, which are suitable and large enough for the simultaneous application of temperature and pressure particularly useful for casting aluminum alloys, often on medium to high strength printing plates that limit still further ver-14 kp / mm ² or less. Since these pressures are subjected to driving steps, z. B. heat in connection with the improved process * cast aluminum alloys to be treated. The proportions are relatively low, the duration of the application of the temperature and the isostatic pressure application is slightly longer than the permissible at higher kes does not affect the behavior of the casting compound at pressures. - · a solution heat treatment. Solution annealing and hot

Casting compounds which can be cured according to the foregoing or other heat treatments can be treated at maintained temperature and isostatic pressure without loss of pressure due to the practical implementation, show advantages over similar, 30 granted to the invention, however, casting compounds not treated in this way have advantages. In fact, the molding compound can, as the applied, improved fatigue strength. The both at sand temperature range when exercising the isostatic as well as at. permanent molding compounds. Pressure the improvement ended near arrive at the solution heat treatment is generally at least can, immediately after the treatment under isostatic 25%, although improvements ₀ or 35 ° pressure / quenched as from 50 to 100, that no Ausmehr often be achieved. This is when the most significant divorce takes place. Artificial aging can. Change in properties compared to non-treated then follow. To be viewed after treatment under isostatic delten casting compounds. Although the tensile pressure can also be made a separate heat treatment to a certain extent improved development. The molding compound may be considered at random in comparison with the machining of any stage before or after the application of the imprinted improvement in fatigue strength as isostatic pressure. For example, a raw sand cast can be machined

The improved casting compounds retain the basic machined, as suggested here improved, heat-generating Advantages of an internal cast structure. treated and then refined if necessary. Photomicrographs Before and After Printing 45 The following are illustrative examples show that there was no visible deformation of the grains of the invention, occurs and the casting compounds their characteristic given grain size, shape and orientation according to example use of isostatic pressure. the

isotropic property characteristics of an inner 50. The casting composition of a completely gußumkleideten diesel-cast structure, that is, a general uniform bean engine piston of an aluminum alloy which spruchungs- and corrosion resistance, strength, the information pursuant to 4.5 ° / ₀ copper, 1.5 ° / o magnesium, and other properties remain in all directions, and contained 2 ° / ₀ nickel, was obtained in a permanent form in a similar manner. . manufactured. The piston casting compound measured about 13.97 cm - one observed on metallographic examination - 55 in diameter and 16.51 cm in height. A noteworthy difference in the improved cast casing was constructed, but the piston cast is that the microporosity was able to accommodate in its bulk so that other than the upper assembly is substantially eliminated. It is common to all- outer surface of the piston head of the piston that there was cast products made of aluminum. The casting compound was heated to 454.5 ° C nium or aluminum alloy to a certain degree and arranged in the preheated casing to show microporosity, regardless of the precaution. A smooth-faced ram was struck into the upper one to avoid the same. End of the casing inserted so that it could be moved away from the improved casting compounds are essentially full - the flat upper outer surface of the piston head got free of micropores of a size over 2.54 μ. The ram, which was the whole of a size which quickly covered at 500 times the piston head, was very much recognizable by the distortion in molding compounds which were not formwork space according to the invention, so that some metal had been treated. The exit between the ram and the casing to size 2.54 μ is intended to express that a minimum was limited. The ram was

Pressed into the casing by means of a hydraulic press of 500 tons for ¹ _1/2 minutes and exerted a pressure of over 32.9 kp / mm ² on the piston. This pressure was essentially isostatic as there was virtually no metal movement. Since the casing and the piston were fitted closely to one another, the amount of mass that could be observed at the piston head was practically zero. . Photomicrographs confirmed the absence of any significant metal movement, as well as no recognizable grain destruction. The micrographs also showed complete freedom from micropores larger than 2.54μ. Several such pistons were cut into pieces from which RR Moore rotating carriers were machined as fatigue test pieces. The fatigue test and the specimens based on it are well known in the art and are described in American Society for Testing Materials Special Technical Publication No. 91, "Manual en Fatigue Testing," 1949. Machine-made tensile specimens were also made from the pistons, ίο The results of the tensile and fatigue tests are included

. Similar tests carried out with pistons in the "as-cast state" are compared in Table 1 been. .

■ ■. Fatigue strength
(kp / mm ^a )
5 x 10 "turns Table 1 Yield strength
(kg / cm ¹ ) % Strain*
Sample length 5.08 cm Status 63.0
11.9 tensile strenght
(kp / mm ² ) 18.2
18.2 0.7
1.6 In the as-cast state
Improved 18.9
23.1

*) Defined by ASTM.

It can be seen that the fatigue strength of the improved molding compositions is almost twice that of unimproved putties. There is also an accidental increase in tensile properties obviously.

Example2

The potting compound of a partially lined piston, which had a cast ring insert near its top periphery, was improved by the method set forth. The band-like ring insert was composed of the well-known cast iron-nickel alloy Ni-Resist, which is often used for this purpose. With the exception of the ring insert, the general size and alloy composition of the piston was identical to that of the fully jacketed piston from Example 1. A formwork with a tightly fitting ram part as in Example 1 was produced. Each casting compound was heated to 454.5 ° C., placed in the preheated casing and the ram _{pressed into the casing against the piston head V for 2} minutes by means of a hydraulic press of 700 tons, creating an essentially isostatic pressure of approximately 37.8 kp / mm ^{2 was} exercised. Fatigue specimens were made from the piston pin fittings of several pistons treated in this way. The fatigue tests showed that the cast aluminum alloy portion of the composite piston design had been improved to the same extent as that of the all-aluminum alloy pistons of Example 1. This is a particularly important embodiment of the invention since iron ring inserts are often included in technical aluminum pistons, especially with heavy loads. Prior to this invention, such an insert, metallurgically bonded, was effected by casting the aluminum piston around the insert, but such pistons were characterized by relatively low fatigue strength, particularly in the critical area of piston stroke. Several schemes have been made for forging the piston around doing the lüiisal /. developed, but this results in a considerably poorer bond than the metallurgical bond which is achieved when the insert is firmly cast in place. Another problem arises from the fact that the forging process often leads to excessive stresses on the ring part, which leads to destruction, breakage or deterioration and failure when commissioned later. The improved pistons retain the advantages of the molded-in insert structure while exhibiting markedly improved fatigue resistance previously only achieved with forged pistons. .

At s ρ i e 1 3

A cylindrical cast iron mold was used to make 15.24 cm in diameter and 20.32 cm long castings of aluminum alloy which were reported to contain 9% silicon, 0.5% magnesium and 1.8% copper. From these, plate-like pieces with a diameter of 13.97 cm and 6.35 cm in length were cut out and machine processed. The pieces were heated to 426.5 to 455 ° C and placed in a tightly fitted preheated casing. A weight of 500 tons was printed on the top of each piece for _{2 minutes by means of a hydraulic press.} The pieces were reheated to 527 ° C and held for 8 hours and then quenched in water at 65.5 ° C, followed by artificial aging for 10 hours at 155 ° C. Fatigue coupons of the type described in Example 1 were made from these, as were pieces that were not subjected to pressure but otherwise identical. In this case, the fatigue tests were carried out at a load of 14.0 kgf / mm ² and the service life of the comparative test pieces was extrapolated to the fatigue strength at 5 · 10 ⁸ revolutions. The tensile properties were also compared again. The results of these tests are shown in Table 2. It can be seen that the test pieces show an improvement in fatigue strength of 33% compared to the "Gul.i-Malerial".

table

Status Logarithmic mean
Fatigue life at
14.0 kg / mm ²
(Revolutions) Extrapolated fatigue
strength in kp / mm ²
5 · 10 ⁸ revolutions tensile strenght
kp / mm ² Yield point
kp / mm ² % Strain VIs cast 460,000
2,354,700 12.0
16.0 32.48
33.25 27.30
27.86 2.1
2.5 Improved

Example 4

Cast flasks of the same size and composition as in Example 1 were placed in an autoclave and ^{exposed to a helium pressure of 10.50 kp / τητη a} at a temperature of about 483 ° C. for about 2 hours. The results of the RR Moore fatigue test with specimens removed from the piston pin fittings of these pistons showed a log mean fatigue life of 1.5 x 10 ⁸ revolutions at a load of 14.0 kp / mm ² , which extrapolates a fatigue strength of 10 , 5 kp / mm ² at 5 · 10 ⁸ revolutions. That is, almost the same improvement was achieved as with the application of mechanical pressure according to Example 1.

209532/108

Claims (4)

1 2 temperature, an isostatic pressure of at least! Claims: 2.1 kp / mm2 is exposed. Under isostatic pressure, an in essence becomes 1. Process for the production of cast bodies borrowed uniform pressure from all sides, anal made of aluminum or aluminum alloys with S understood the hydrostatic pressure on a body immersed in resting improved fatigue strength and a micro-liquid. While the pore size is not more than 2.54 microns, while the pressure is at least 2.1 kp / mm ² , characterized in that the casting should be, a pressure range of at least 315 ° is preferred C, 3.5 kp / mm ³ and higher, for example 7.0 to 70 kp / mm but below the melting temperature, an io used. Slightly higher temperatures than above isostatic pressure of at least 2.1 kp / mm ² are permitted, although the temperature is not exposed. should be so high that melting occurs. De 2. The method according to claim 1, characterized marked preferred temperature range is 371-638 ° (is characterized in that the cast body at a pressure of 7 Lower temperatures are preferably ver to 70 kgf / mm ² at a temperature of 371 -mieden to 15, as constant improvement is not exposed to 638 ° C. substantial difficulties can be achieved 3. The method according to claim 1, characterized in that, according to the foregoing, invention records that a pressure of 3.5 to 14 kp / mm ^2, the casting compound temperature and pressure is exerted hydrostatically and exposed to areas for at least one hour which is normally maintained on. 20 are turned to avoid essential metal movements 4. The method according to claim 1 or 2, to cause. However, in practice it is characterized in that an isostatic pressure guide of the invention ^{essentially avoids such a metal movement: from 14 to 70 kp / mm 2} due to the shape of the. Cast body-adapted formwork exerted an important feature in the practical through and is maintained for at least 15 seconds. 25 management of the invention is that the iso static pressure on the entire casting compound for a certain period of time, e.g. B. several seconds up to 1 hour or more. This can be de: in a forging process occurring Situatior 30 are compared, where a given pressure The invention relates to a method of manufacturing mirrors that do not usually weigh on the entire part of castings made of aluminum or aluminum and usually not during a significant one alloys with improved fatigue strength and durability is maintained. When forging is that a micropore size no greater than 2.54 microns. Pressure application either very briefly, as with In the manufacture of different types of parts or impact forging, or is immediately reduced by metal molds made of aluminum or aluminum alloys, movement, or both is given. In the case of particularly complex shapes, in those practicing the invention, where a choice is made, the smallest period of pressure application may almost always be considered to be somewhat dependent on the isostatic pressure level due to the cost savings over forging and casting other methods. Since higher isostatic pressures can be maintained for shorter periods of time, which is advantageous for aluminum or aluminum alloy casting compounds, there are, however, certain disadvantages which make their application more than lower pressures. The temperature is another twist limit. One such limitation, the dependent factor, since higher temperatures adhere to such engineered castings, partial use of lower pressures, shorter times, is that their fatigue strength is significantly inferior to that of forged compounds for the application of pressure or both. For verification, various measures can be taken during the practical demonstration: A forging mass shows in general implementation of the invention for the exercise of what is believed to be a fatigue strength of 25% or more, isostatic pressure can be used. The measures that are greater than those of a corresponding casting compound are mechanical pressure. In this description, fatigue strength is understood to mean application, such as through formwork (molds) and exercise, the stress that is required for an application of liquid pressure, such as through a gas. predetermined number of revolutions can be applied without failure in the mechanical exercise of the isostatic. In the aluminum industry, pressure is applied to the casting compound within one of the casts.It is customary to place the fatigue strength as a formwork adapted to the dimensions, resistance to stress at 5 · 10 ⁸ revolutions without 55 The pressure can then be determined by any dimensional failure. took as if exercised by a hydraulic press The invention was based on the object of becoming. It is important that the formwork for the production of castings from aluminum is constructed so that essentially a metal flux or aluminum alloys are prevented from developing in the casting compound, ie the casting compound softens an improved fatigue strength, in which 60 must so be included that should be substantially any order of magnitude of 25 ° / ₀ or more. significant movement from it is prevented. So are This object was achieved with a method for conventional forging formwork in general position of cast bodies made of aluminum or aluminum with regard to smooth outer surfaces or others minium alloys with improved fatigue strength points for metal leakage from the casing, speed and a micropore size not exceeding 65 which eliminates the isostatic pressure by metal 2.54 Micron solved, which would be evaded by movement, to modify something, is that the cast body is at a temperature of Da the mechanically applicable isostatic pressure at least 315 ° C, but below the melting point is limited only by the pressing capacity