EP2927335B1 - Aluminium bronze alloy, method for manufacturing the same and product made of aluminium bronze - Google Patents

Description

The invention relates to an aluminum bronze alloy and to a production process for an aluminum bronze alloy. Further, the invention deals with a product of such an aluminum bronze.

The requirements for alloys for friction applications, such as those for piston liners or thrust bearings of a turbocharger, are manifold. A suitable alloy must have a low coefficient of friction in order to minimize the power dissipation caused by the friction and to reduce the heat development in the area of the friction contact. Furthermore, it should be noted that for typical applications, the friction partners are in a lubricant environment, where in principle a good adhesion of the lubricant to the alloy is required. In addition, upon contact with the lubricant under frictional loading, a stable tribological layer is to be formed, which, like the subordinate base matrix of the alloy, must have high thermal stability and good thermal conductivity. In addition, a broadband oil compatibility is required, so that a substantial insensitivity of the alloy and the tribological layers to changes in the lubricant results.

Furthermore, the objective is to provide a high mechanical strength alloy, which has a sufficiently high 0.2% proof strength to keep plastic deformation under load low. Furthermore, a high tensile strength and hardness must be present so that the alloy withstands abrasive and adhesive loads. The dynamic load capacity should be so high that a good toughness against impact stresses is given. In addition, the highest possible fracture toughness slows down the crack growth rate starting from microdefects, with an alloy being required which is as free of residual stresses as possible in terms of defect growth.

Suitable alloys for components with a tendency to rust are in many cases special brasses which, in addition to copper and zinc as main constituents, are an alloy at least one of the elements nickel, iron, manganese, aluminum, silicon, titanium or chromium. In particular, silicon brasses meet the above-mentioned requirements, with CuZn31Si1 representing a standard alloy for friction applications, for example for piston liners.

It is also known to use tin bronzes, which in addition to tin and copper additionally nickel, zinc, iron and manganese, for Reibanwendung or for mining applications. Another class of alloys of interest for friction-loaded components are aluminum bronzes, which, in addition to copper and aluminum, may contain alloying additives selected from the group consisting of nickel, iron, manganese, aluminum, silicon, tin and zinc. The result for faster moving friction loaded components when using aluminum bronzes, the additional advantage of a weight reduction due to the light element aluminum. With regard to components as friction-loaded components made of brass or gunmetal, the components produced from the previously known aluminum bronzes are only suitable for relatively slowly moving friction components.

A use of a copper-aluminum alloy with a cover layer of aluminum oxide for use as a bearing material for the production of a sliding bearing is known from DE 101 59 949 C1 known. An aluminum content of 0.01 to 20% and the use of further choice elements from the group of iron, cobalt, manganese, nickel, silicon, tin up to a maximum of 20% and optionally up to 45% zinc are disclosed. Other broadband alloy compositions for silicon bronze are by US 6,699,337 B2 . JP 04221033 A and DE 22 39 467 A such as JP 10298678 A described.

Another alloy composition is off US 3,923,500 known.

The object of the invention, based on the prior art outlined above, is to propose an aluminum bronze alloy and a product of an aluminum bronze alloy, which are distinguished by improved mechanical properties and, in particular, by good adjustability of the material parameters to the present static and dynamic load. In addition to a high corrosion resistance, good oil compatibility and high thermal stability and sufficient thermal conductivity at the same time be given low weight. Furthermore, a method for producing an aluminum bronze alloy and a product from an aluminum bronze alloy must be specified.

• 7,0 - 10,0 Gew.-% Al;
• 3,0 - 6,0 Gew.-% Fe;
• 3,0 - 5,0 Gew.-% Zn;
• 3,0 - 5,0 Gew.-% Ni;
• 0,5 - 1,5 Gew.-% Sn;
• ≤ 0,2 Gew.-% Si;
• ≤ 0,1 Gew.-% Pb;

und Rest Cu.The above object is achieved by a Aluminiumbronzelegierung with

• 7.0 - 10.0% by weight Al;
• 3.0-6.0 wt% Fe;
• 3.0 - 5.0 wt% Zn;
• 3.0 - 5.0 wt% Ni;
• 0.5-1.5 wt% Sn;
• ≦ 0.2 wt% Si;
• ≦ 0.1% by weight of Pb;

and balance Cu.

• 7,0 - 9,0 Gew.-% , insbesondere 7,0 - 7,8 Gew.-% Al;
• 4,0 - 5,0 Gew.-% Fe;
• 3,8 - 4,8 Gew.-% Zn;
• 3,8 - 4,1 Gew.-% Ni;
• 0,8 - 1,3 Gew.-% Sn;
• ≤ 0,2 Gew.-% Si;
• ≤ 0,1 Gew.-% Pb;

und Rest Cu.An improvement of the desired properties can be achieved again if the aluminum bronze alloy has the following composition:

• 7.0-9.0% by weight, especially 7.0-7.8% by weight Al;
• 4.0-5.0% by weight of Fe;
• 3.8-4.8% by weight of Zn;
• 3.8-4.1% by weight of Ni;
• 0.8-1.3 wt% Sn;
• ≦ 0.2 wt% Si;
• ≦ 0.1% by weight of Pb;

and balance Cu.

All of the alloy compositions described in this specification may contain unavoidable impurities per element of 0.05% by weight, the total amount of impurities should not exceed 1.5% by weight. However, it is preferred to keep the impurities as low as possible and not exceed a proportion of 0.02 wt .-% per element, a total amount of 0.8 wt .-%.

For a particularly advantageous embodiment, the ratio between aluminum and zinc based on the weight fractions in the aluminum bronze alloy in a range of 1.4-3.0, and more preferably between 1.5 and 2.0.

The lead content of the alloy is preferably less than 0.05 wt .-%. The alloy is thus lead-free except for unavoidable impurities.

The alloy is also manganese-free except for unavoidable impurities. That this alloy has the particular properties described below was also surprising in view of the background that prior art low-zinc alloyed copper alloys regularly contain manganese as a mandatory alloying element to achieve the desired strength properties.

Essential in the claimed alloy is the combination of the alloying elements aluminum, nickel, tin and zinc in the proportions described. Particularly preferred is an embodiment in which the sum of these elements is not less than 15 wt .-% and not greater than 17.5 wt .-%.

The composition of the aluminum bronze alloy according to the invention leads to an alloy matrix having a dominant α phase in the case of hot forming following the alloy melt and subsequent cooling below 750 ° C. In the following, this state is referred to as extruded state. In this case, the chemical composition of the aluminum bronze alloy is preferably adjusted so that in the extruded state, the fraction of the β-phase is less than 1% by volume of the alloy matrix. This alloy solidifies from the melt virtually directly in the α-β-two-phase space. This results in the hot working, preferably an indirect extrusion, for the α-phase to a dynamic recrystallization followed by a static recrystallization, which gives rise to a fine alloy structure. For the β-phase portion, the recrystallization process in hot working proceeds via dynamic recovery followed by static recrystallization. In addition, κ _II and / or κ _IV phases occur with iron and / or nickel aluminides.

Here, the structure present in the extruded state is not only characterized by the choice of aluminum content, but also determined by the other alloyed elements. For iron, a grain-refining effect is to be assumed. Tin has a stabilizing effect on the β-phase before the state of extrusion with the structure essentially determined by the α-phase is reached near the boundary to the α-β mixed phase. In this case, the selected ratio of aluminum to zinc has proved to be relevant for the state of extrusion and the resulting adjustability of the mechanical properties by subsequent cold forming and heat treatment steps.

Compared to a conventional, used for reibbelastete components alloy of the type CuAl10Ni5Fe4 proves to be an advantage in the claimed alloy that at the same temperature control of a heat-retentive treatment above the recrystallization threshold after cooling this has significantly lower β-phase components. Therefore, a product made of such an alloy is significantly more corrosion resistant than a product made from the aforementioned prior art alloy. Especially for such applications, the relatively high zinc content is also positively noticeable, since this allows higher sliding speeds.

Investigations have shown that the special properties of the claimed aluminum bronze alloy no longer exist if the narrowly stressed areas in one or more of the compulsory elements are exceeded or even exceeded. Surprisingly, these investigations result in the prescribed special alloy matrix having the very dominant α phase and a β phase which is only inferior in volume, if present, only in the claimed range.

Furthermore, it has been found that, starting from the extruded state, high work hardening is possible for a product of the aluminum bronze alloy according to the invention which leads to a substantial increase in the 0.2% yield strength R _P0.2 and the tensile strength R _m . This extensive hardening during cold forming reduces the reserve of the alloy for plastic deformation. The concomitant reduction The elongation at break can be increased for the alloy according to the invention by a final annealing in a temperature range from 300 to about 500 ° C with a temperature setting below the solution annealing temperature. During the final annealing, no reduction in the 0.2% proof strength and tensile strength occurs; instead, contrary to expectations, there is a further increase in strength.

For heat treatment steps carried out after the extrusion state has been reached so that the temperatures used are below the recrystallization threshold and within the α-phase solubility range, there is no change in the phase composition of the matrix of the extrusion state. Nevertheless, there is a surprisingly broadband adjustability of the mechanical parameters for a heat treatment in this temperature range, so that a highly loadable and adaptable product of the aluminum bronze alloy _{according to} the invention with a 0.2 yield strength R _P0.2 in the range of _650-1000 MPa, a tensile strength R _m in Range of 850 - 1050 MPa and an elongation at break A ₅ in the range of 2 - 8% and preferably in the range of 4 - 7% is formed. Preferably, after the hot and cold working and the final annealing, a final alloy state results, which additionally has a yield ratio SV in the range of 85-95% and a Brinell hardness of 250-300 HB 2.5 / 62.5.

The product of the aluminum bronze alloy according to the invention, when in contact with a wide range of lubricants under frictional loading, forms stable tribological layers, in which aluminum oxide, in addition to aluminum oxide, is incorporated in conjunction with lubricant components, and into which a sufficient runflat resistance-inducing tin diffuses. In addition, Hartphasenausscheidungen are in the form of intermetallic κ _II and / or κ _IV phases with iron and / or nickel aluminides, which represent highly resilient contact points of the friction layer in a ductile matrix.

The aluminides are preferably formed at the grain boundaries of the α-matrix of the alloy, wherein in the final alloy state the mean grain size of the α-matrix is ≦ 50 μm. The intermetallic κ _II and / or κ _IV phases take an elongated shape with a middle one due to the alloying Length of ≤10 microns and a median volume of ≤1,5 microns to ^2, wherein is carried out at a hot forming by indirect extrusion in an alignment direction of stretching which is hardly affected by the subsequent cold forming. Further, additional aluminide precipitation is observed leading to intermetallic phases having a roundish shape and a small average size of ≦ 0.2 μm in the final alloy state after the final annealing.

The method according to the invention starts from the abovementioned alloy composition according to the invention and uses a hot forming method, preferably an indirect extrusion, after the melting of the alloy constituents. The subsequent cold forming is carried out according to an advantageous embodiment as cold drawing with a degree of deformation in the range of 5 - 30%.

Particularly preferred is an alloy composition which results in an extrusion state which, after cooling, allows direct cold working without further heat treatment. Thus, the final alloy state of a product of the aluminum bronze alloy, and particularly preferably already the state of extrusion, has an α-matrix with a maximum β-phase content of 1% by volume. If the β-phase content in the extrusion state is higher, alternatively, soft annealing may be carried out in a temperature range of 450-550 ° C. between hot working and cold working.

The final annealing after the cold working step is selected in terms of temperature so that the alloy is tempered under the solution annealing temperature in a range of 300 - about 500 ° C. However, preferred is an embodiment in which this heat treatment step is carried out only up to a maximum temperature of 400 ° C. As a result, a 0.2% proof stress in the range of 650-1000 MPa, a tensile strength R _m in the range of 850-1050 MPa and an elongation at break A ₅ in the range of 2-8% and preferably in the range of 4-7% adjusted without using a temperature-controlled cooling. The final annealing mainly affects the elongation at break A ₅ , so that it can be selectively and broadband adjustable. The 0.2% proof stress and the tensile strength R _m are calculated from a defined extrusion state selected in particular by the choice of the degree of deformation during cold drawing.

The alloy according to the invention is suitable for constant frictional loads as well as due to its special properties, especially for the production of a component on which a time-varying frictional load acts, such as a bearing bush for a bearing of a piston shaft, a sliding block or a highly reibbelastetes worm wheel. Another possible use of a component made of the alloy is a thrust bearing for a turbocharger. A time-varying friction load can also lead to a lack of lubrication, wherein the tin content contained in the alloy ensures that the exposed to such a load component meets the relevant requirements.

Fig. 1:

eine rasterelektronenmikroskopische Aufnahme der erfindungsgemäßen Aluminiumbronzelegierung mit 3000-facher Vergrößerung,

Fig. 2:

eine rasterelektronenmikroskopische Aufnahme der erfindungsgemäßen Aluminiumbronzelegierung mit 6000-facher Vergrößerung,

Fig. 3:

eine rasterelektronenmikroskopische Aufnahme der erfindungsgemäßen Aluminiumbronzelegierung mit 9000-facher Vergrößerung.

In the following the invention will be explained with reference to a preferred embodiment with reference to the figures. Show it:

Fig. 1:

a scanning electron micrograph of the aluminum bronze alloy according to the invention with 3000 times magnification,

Fig. 2:

a scanning electron micrograph of the aluminum bronze alloy according to the invention with 6000 times magnification,

3:

a scanning electron micrograph of the aluminum bronze alloy according to the invention with 9000-fold magnification.

For one embodiment of the invention, the alloy composition was melted and hot worked by means of vertical continuous casting at a casting temperature of 1170 ° C and a casting speed of 60 mm / min. At a press temperature of 900 ° C.

The relevant alloy has the following composition: Cu Zn pb sn Fe Mn Ni al rest 4.64 0.01 1.01 4.08 0.03 3.90 7.30

The experimental alloy obtained after cooling in the extruded state was characterized by means of scanning electron micrographs and energy-dispersive analyzes (EDX) Figures 1 and 2 shown material state was present. The in the Figures 1 and 2 shown with secondary electron contrast at the magnifications 3000x and 6000x show an α-phase, which forms the alloy matrix, and hard phase precipitates in the form of K _II and K _IV phases, which consist of iron and nickel aluminides and which are mainly at the grain boundaries deposit. Furthermore, the in FIG. 3 shown recording with a 9000-fold magnification, that in addition Hartphasenausscheidungen present with a mean size of ≤ 0.2 microns.

For the α phase, EDX measurements averaged a chemical composition of 84.2 wt% Cu, 5.0 wt%. Zn, 4.4% by weight. Fe, 3.4% by weight. Ni, 2.8% by weight. Al and 0.1% by weight. Si. For the κ _II phases investigated, the average composition was 15.2% by weight Cu, 2.4% by weight, in the extruded state. Zn, 67.6% by weight. Fe, 9.4% by weight. Ni, 4.7% by weight. Al and 0.7% by weight. Si found. Further, the content of the intermetallic phases was determined to be 7% by volume while the phase-order β-phase content was less than 1% by volume. Measurements of the material states resulting from the cold working and heat treatment steps shown below did not change the phase composition.

To set the mechanical properties, starting from the state of extrusion determined essentially by the chemical composition of the aluminum bronze alloy, an annealing at 550 ° C. was carried out, followed by cold forming in the form of stretch drawing. The soft annealed intermediates were prepared in a soap bath at 50 ° C for cold drawing. As process parameters, different cross-section reductions (QM) of 8 - 25% were chosen for stretch drawing. In a final treatment step, a final annealing of the converted aluminum bronze products was carried out at 380 ° C. for 5 hours, the mean being the mechanical properties summarized in Table 1 for the 0.2% yield strength R _P0.2 , the tensile strength R _m , the elongation at break A ₅ , the Brinell hardness HB and the yield ratio were: Status R _P0,2 [MPa] R _m [MPa] A ₅ [%] HB 2.5 / 62.5 SV [%] Extruded state 360 690 26 176 48.8 Cold forming 8% QM 700 810 9.6 211 85.7 Cold forming 15% QM 840 840 6.1 225 86.9 Cold forming 20% QM 850 930 5.5 233 91.2 Cold forming 25% QM 830 950 3.9 242 87.0 Final annealing 380 ° C / 5h (after 8% QM) 830 870 5.9 250 95.1 Final annealing 380 ° C / 5h (after 15% QM) 810 900 6.5 260 90.3 Final annealing 380 ° C / 5h (after 20% QM) 850 930 5.5 275 91.2 Final annealing 380 ° C / 5h (after 25% QM) 940 1000 2.5 291 94.1

Final annealing to adjust the final alloy state of the aluminum bronze products was performed for further series of measurements below the mild or solution annealing temperature. For the experiments, preferably final annealing temperatures in the range of 300-400 ° C were selected, in combination with a variation of the degrees of extraction of the upstream cold forming a wide range for the mechanical properties of the final alloy state is adjustable without applying costly measures for temperature-controlled cooling.

The description of the invention, also with reference to the concrete embodiment, makes it clear that the special, positive properties The claimed invention was not to be expected in the background of the prior art disclosures in the narrow claimed region of the elements involved in the alloy. It was therefore surprising for the inventor to find that by adjusting the alloying parameters in the claimed interval over that known from prior art alloys, such are improved. This also applies in view of the surprisingly robust processability of this alloy for setting the desired strength properties.

Claims (16)

1. Aluminium bronze alloy, with

   7.0 - 10.0 % by weight Al;

   3.0 - 6.0 % by weight Fe;

   3.0 - 5.0 % by weight Zn;

   3.0 - 5.0 % by weight Ni;

   0.5 - 1.5 % by weight Sn;

   ≤ 0.2 % by weight Si;

   ≤ 0.1 % by weight Pb;

   and the remainder Cu together with unavoidable impurities.
2. Aluminium bronze alloy according to claim 1, with

   7.0 - 7.8 % by weight Al;

   4.0 - 5.0 % by weight Fe;

   3.8 - 4.8 % by weight Zn;

   3.8 - 4.1 % by weight Ni;

   0.8 - 1.3 % by weight Sn;

   ≤ 0.2 % by weight Si;

   ≤ 0.1 % by weight Pb;

   and the remainder Cu together with unavoidable impurities.
3. Aluminium bronze alloy according to any one of claims 1 or 2, characterised in that the proportion between aluminium and zinc related to the weight portions in the aluminium bronze alloy lies in a range of 1.4 - 3.0, and for particular preference between 1.5 and 2.0.
4. Aluminium bronze product with an alloy composition according to any one of claims 1 to 3, characterised in that the product is adjusted, by way of final annealing following cold forming leading to an alloy terminal state, in a temperature range from 300-500 °C, in such a way that the 0.2 % elongation limit R_p0.2 lies in the range of 650-1000 MPa, the tensile strength R_m lies in the range of 850-1050 MPa, and the elongation after fracture A₅ lies in the range of 2-8%, and preferably in the range of 4-7%.
5. Aluminium bronze product according to claim 4, characterised in that in the alloy terminal state the ratio of yield point to tensile strength SC lies in the range of 85-97%.
6. Aluminium bronze product according to any one of claims 4 or 5, characterised in that in the alloy terminal state the hardness lies in the range of 250-300 HB 2.5/62.5.
7. Aluminium bronze product according to any one of claims 4 or 5, characterised in that in the alloy terminal state an α-matrix with a maximum β phase portion of 1% by volume pertains.
8. Aluminium bronze product according to claim 7, characterised in that in the alloy terminal state the mean grain size of the α-matrix is ≤ 50 µm.
9. Aluminium bronze product according to any one of claims 4-8, characterised in that in the alloy terminal state intermetallic K_II and/or K_IV phases with iron and/or nickel aluminides are present.
10. Aluminium bronze product according to claim 7, characterised in that in the alloy terminal state the intermetallic K_II and/or K_IV phases exhibit a longitudinal form with a mean length of ≤ 10 µm and a mean volume of ≤ 1.5 µm².
11. Aluminium bronze product according to any one of claims 4-10, characterised in that in the alloy terminal state an aluminide precipitation with a circular form and a mean size of ≤ 0.2 µm.
12. Aluminium bronze product according to any one of claims 4 to 11, characterised in that the product is a component designed for a time-variable friction loading, in particular a bearing sleeve, a sliding shoe, a worm wheel, or an axial bearing.
13. Method for manufacturing a product made from an aluminium bronze with the method steps:

    - Manufacture of a cast blank from a melt with the alloy constituents:

    7.0 - 10.0 % by weight Al;

    3.0 - 6.0 % by weight Fe;

    3.0 - 5.0 % by weight Zn;

    3.0 - 5.0 % by weight Ni;

    0.5 - 1.5 % by weight Sn;

    ≤ 0.2 % by weight Si;

    ≤ 0.1 % by weight Pb;

    and the remainder Cu together with unavoidable impurities;

    - hot forming of the cast blank to an intermediate product; cold forming of the intermediate product, and

    - final annealing of the product below the solution annealing temperature in a temperature range of 300-500 °C, wherein, after the final annealing, the 0.2 % elongation limit Rp_0.2 lies in the range of 650-1000 MPa, the tensile strength R_m lies in the range of 850-1050 MPa, and the elongation after fracture A₅ lies in the range of 2-8%, and preferably in the range of 4-7%.
14. Method according to claim 13, characterised in that the melt for the production of the cast blank exhibits the following composition:

    7.0 - 7.8 % by weight Al;

    4.0 - 5.0 % by weight Fe;

    3.8 - 4.8 % by weight Zn;

    3.8 - 4.1 % by weight Ni;

    0.8 - 1.3 % by weight Sn;

    ≤ 0.2 % by weight Si;

    ≤ 0.1 % by weight Pb;

    and the remainder Cu together with unavoidable impurities.
15. Method according to any one of claims 13 or 14, characterised in that the hot forming is carried out as indirect extrusion pressing.
16. Method according to any one of claims 13 - 15, characterised in that the cold forming is carried out as cold drawing with a forming degree of 5-30%.

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