METHOD FOR MANUFACTURING A METAL COMPONENT, METAL COMPONENT, AND TURBOCHARGER

Abstract

A turbocharger compressor wheel with an aluminum proportion of at least 50 atom percent, produced by. etching a turbine wheel base body using an alkaline etchant to produce a specific etch pitting consisting of nano pores and micropores and chemical deposition of a nickel-phosphorous protective layer (19) onto the etched base body surface.

Claims

1. A method for manufacturing a compressor wheel (17) for a turbocharger (1), the compressor wheel (17) comprising a base body and a nickel-phosphorous protective coating, the method comprising the steps: etching the base body using an alkaline etchant to produce a specific etch pitting, wherein said specific etch pitting consists of nano etch pittings and micro etch pittings, wherein the nano etch pittings have a depth of 0.1 to 1.5 μm and micro etch pittings have a depth of 4 to 12 μm, and chemical deposition of a nickel-phosphorous protective layer (19) onto the etched metal surface, wherein the nickel-phosphorous protective layer comprises phosphorous, antimony and nickel.

2. The method according to claim 1, wherein the etching is carried out in an etching bath.

3. The method according to claim 2, wherein a temperature of the etching bath lies between 50 and 80° C.

4. The method according to claim 2, wherein an immersion time of the base body into the etching bath is between 20 and 40 seconds.

5. The method according to claim 2, wherein a dwell time of the base body in the etching bath is 60 to 110 seconds.

6. The method according to claim 2, wherein the base body is moved in the etching bath in a radially extending circular path.

7. The method according to claim 6, wherein a rotational speed of the base body in the etching bath is 10-15 rpm.

8. The method according to claim 1, wherein a coating composition is used for the chemical deposition which contains nickel ions, more than 10.3 wt. %, of phosphorous, and more than 0.3 wt. % of antimony, maximum 0.5 wt. % antimony, in each case relative to the total weight of the coating composition.

9. The method according to claim 1, wherein the base body is treated with a nitric acid solution prior to the chemical deposition of the nickel-containing layer.

10. The method according to claim 1, wherein the base body is formed from AlCuMgNi or AlCu.sub.2MgNi.

11. A compressor wheel (17) for a turbocharger (1), the compressor wheel (17) having a base body and a nickel-phosphorous protective coating (19), the base body having an aluminum proportion of at least 50 atom percent, the base body having a specific etch pitting, wherein said specific etch pitting consists of nano etch pittings and micro etch pittings, wherein the nano etch pittings have a depth of 0.1 to 1.5 μm and micro etch pittings have a depth of 4 to 12 μm, and wherein the nickel-phosphorous protective coating (19) contains nickel, phosphorous, and more than 0.3 wt. % of antimony relative to the total weight of the coating composition.

12. The compressor wheel according to claim 11, wherein the coating (19) has a layer thickness variation of maximum±1.5 μm and a layer thickness of the coating (19) of approximately 20 μm.

13. (canceled)

14. (canceled)

15. The compressor wheel according to claim 11, wherein a volume ratio of the nano pittings to the micro pittings is 15:1 through 20:1.

16. A turbocharger comprising the compressor wheel according to claim 11.

17. A compressor wheel according to claim 11, wherein the coating composition is comprised of more than 10.3 wt. % phosphorous, and more than 0.3 wt. % of antimony, balance nickel, in case relative to the total weight of the coating composition.

18. A compressor wheel according to claim 11, wherein the coating composition is comprised of more than 10.5 wt. % phosphorous, and more than 0.3 wt. % but maximum 0.5 wt % antimony, balance nickel, in each case relative to the total weight of the coating composition.

Description

[0030] Additional details, advantages, and features of the present invention arise from the subsequent description of embodiments by means of the drawings.

[0031] FIG. 1 shows a partial sectional view of a turbocharger according to one embodiment of the invention,

[0032] FIG. 2 shows a microscopic sectional view of a section of a metal component according to one embodiment of the invention, and

[0033] FIG. 3 shows a diagram to illustrate the mechanical strength of the metal component according to the invention from FIG. 2.

[0034] FIG. 1 shows a perspective view presented with partial cut aways of an exhaust gas turbocharger according to one embodiment of the invention. A turbocharger 1 is depicted in FIG. 1 which has a turbine housing 2 and a compressor housing 3 connected thereto via a bearing housing 28. Housings 2, 3, and 28 are arranged along an axis of rotation R. The turbine housing is shown with partial cut aways in order to clarify the arrangement of a blade bearing ring 6 and a guide baffle 18 formed radially outwardly by the same and which has a plurality of guide vanes 7 distributed across the circumference, and the guide vanes have pivot axes 8. By this means, nozzle cross sections are formed which are larger or smaller according to the position of guide vanes 7 and which impinge turbine wheel 4, mounted in the center at axis of rotation R, with more or less exhaust gas of an engine supplied via a supply channel 9 and discharged via a central nozzle 10 in order to drive compressor wheel 17 seated above turbine wheel 4 on the same shaft.

[0035] In order to control the movements or the position of guide vanes 7, an actuation unit 11 is provided. This may be designed in any way, for example in the form of a control housing 12 which controls the control movement of a tappet part 14 fixed to it in order to convert the movement of the tappet part on an adjustment ring or holding ring 5, mounted behind the blade bearing ring 6, into a slight rotational movement of the adjustment ring or holding ring. A clearance 13 for guide vanes 7 is formed between blade bearing ring 6 and an annular part 15 of turbine housing 2. In order to be able to ensure this clearance 13, blade bearing ring 6 has spacers 16.

[0036] Compressor wheel 17 is a metal component in the context of the present invention and is formed from a metal material which contains at least 50 atom percent aluminum. Compressor wheel 17 has a nickel-containing coating 19. Nickel-containing coating 19 contains nickel, more than 10.3 wt. % phosphorous, and more than 0.3 wt. % antimony, in each case relative to the total weight of coating 19. Indentations are formed at the surface of compressor wheel 17, so-called etch pittings which were obtained by corresponding chemical pretreatment of compressor wheel 17 prior to the application of nickel-containing coating 19, for optimizing the adhesion of nickel-containing coating 19.

[0037] FIG. 2 shows in detail a microscopic sectional view of a section of a metal component, more exactly, a section of a compressor wheel 17 according to one embodiment of the invention. For this purpose, a piece of compressor wheel 17 was embedded in an embedding means 21 and examined (microsection examination) by means of scanning electron microscopy (SEM) at a 500× magnification. The reference numeral 20 thereby stands for the metal material, thus a material comprising at least 50 atom percent aluminum. The material is in particular a heat resistant AlCuMgNi or AlCu.sub.2MgNi material.

[0038] To manufacture compressor wheel 17, a compressor wheel manufactured from the AlCu.sub.2MgNi material was etched using an alkaline etchant E6 and a nickel-containing layer 19 was subsequently chemically deposited on the surface of compressor wheel 17. During the etching process, compressor wheel 17 was moved in a radially extending circular path and periodically reversed in its movement direction.

[0039] Due to the etching with selectively effective etchant E6, etch pittings were formed on the surface of the AlCu.sub.2MgNi material. These are indentations which are formed by dissolving primary aluminum and Fe—Cu—Ni precipitation phases and MgSi.sub.2 precipitation phases. Among the indentations are those with a depth of 0.1 to 1.5 μm, so-called nano etch pittings 22, and those with a depth of 4 to 12 μm, so-called micro etch pittings. The proportion of nano etch pittings 22 is thereby decisively relevant for a good adhesion of coating 19 to the surface of metal component 20.

[0040] FIG. 2 shows that nano etch pittings 22 are formed across the entire metal material surface. Nickel-containing coating 19 has sunken into these indentations. Since nano etch pittings 22 have a very small maximum depth, namely a maximum of 1.5 μm, surface 23 of compressor wheel 17 contacting the surroundings of compression wheel 17 is not deformed by the sinking in of coating 19. The surface quality of compressor wheel 17 is thus high.

[0041] Nickel-containing coating 19 contains nickel, more than 10.3 wt. % phosphorous, and more than 0.3 wt. % antimony (maximum 0.5 wt. % Sb), in each case relative to the total weight of coating 19. Coating 19 causes a type of corset effect and adheres very well to metal component 20. The layer thickness was 23 to 28 μm at a layer thickness tolerance of maximum±1.5 μm.

[0042] Compressor wheel 17 was examined for its mechanical strength.

[0043] It was shown hereby that a natural frequency of compressor wheel 17 is increased by 2% in comparison to conventional compressor wheels. This is traced back to the corset effect of nickel-containing coating 19 and the very good interlocking of nickel-containing coating 19 in nano etch pittings 22. Due to the higher natural frequency, unexpectedly high power reserves become accessible in the upper rotational speed range.

[0044] Due to the etching with alkaline etchant E6, which is carried out in an etching bath at a temperature of from 55 to 65° C., an immersion time of approximately 30 seconds, a dwell time of approximately 85 to 95 seconds, and an emersion time of approximately 30 seconds, a uniform distribution of etch pittings is obtained which induces macrogeometrically only marginal changes across the total surface, such that following the coating, a rebalancing of compressor wheel 17 may be omitted. By this means, not only costs may be reduced, but flaws in the coating generated by milling during rebalancing are also prevented. By this means, a permanently stable nickel-containing coating 19 was obtained which also had a very good corrosion resistance even after longer usage of compressor wheel 17.

[0045] The advantageous features of compressor wheel 17 manufactured according to the invention manifested particularly impressively in a so-called spin test. The results of the spin test are presented in the form of a diagram in FIG. 3.

[0046] In the spin test, the compressor wheel, whose microscopic structure is depicted in FIG. 2, was accelerated from 20,000 rpm (revolutions per minute) to 250,000 rpm in a test frame by means of a drive and compressor wheel receiver. This corresponds to one cycle. 10 correspondingly manufactured compressor wheels were examined and the lifecycle results are summarized in FIG. 3 as Result A. A lifecycle for compressor wheel 17 according to the invention was between 27,000 and 30,000 cycles, thus an average of approximately 28,500 cycles. For conventional compressor wheels without the coating applied according to the invention, for example with an electroplated nickel layer, a lifecycle resulted between 11,000 and 18,000 cycles, thus an average of approximately 14,250 cycles (see Result B in FIG. 3). The lifecycle of compressor wheel 17 was thus significantly increased using the coating according to the invention by almost 100%.

[0047] The following validation tests had likewise good results: [0048] Outdoor weathering test [0049] Climatic change test [0050] Bombardment test with dust particles at average rotational speed [0051] Scratch test [0052] Flexural strength test for determining the adhesion and confirming the stability of the coating adhesion

[0053] The hardness of compressor wheel 17 was between 550 HV and 650 HV.

[0054] In addition to the present written description of the invention, explicit reference is made hereby to the illustrated depiction of the invention in FIGS. 1 through 3 as a supplemental disclosure thereto.

LIST OF REFERENCE NUMERALS

[0055] 1 Turbocharger [0056] 2 Turbine housing [0057] 3 Compressor housing [0058] 4 Turbine wheel [0059] 5 Adjustment ring or holding ring [0060] 6 Blade bearing ring [0061] 7 Guide vanes [0062] 8 Pivot axes [0063] 9 Supply channel [0064] 10 Axial nozzle [0065] 11 Actuation unit [0066] 12 Control housing [0067] 13 Clearance for guide vanes 7 [0068] 14 Tappet part [0069] 15 Annular part of the turbine housing 2 [0070] 16 Spacer/distance cam [0071] 17 Compressor wheel [0072] 18 Guide baffle [0073] 19 Nickel-containing coating [0074] 20 Metal component [0075] 21 Embedding means [0076] 22 Nano etch pittings [0077] 23 Surface of the nickel-containing coating [0078] 28 Bearing housing [0079] R Axis of rotation