PROCESS FOR FORMING A SURFACE LAYER ON ALUMINUM AND ALUMINUM ALLOY ARTICLES AND SO FORMED ARTICLES

Abstract: A process for forming a surface layer on aluminum and aluminum alloy articles, characterized by forming on the surface of the article a coating comprising maganese and reaction products of manganese with oxygen and nitrogen or with oxygen, nitrogen and sulphur. An article comprising at least a surface part of aluminum or aluminum alloy, characterized in that the aluminum or aluminum alloy surface is provided with a surface coating comprising manganese and reaction products of maganese with oxygen and nitrogen, or with oxygen, nitrogen and sulphur, preferably as particles dispersed in a manganese surface layer matrix.

Description: "Process for forming a surface layer on aluminum- ' and aluminum alloy articles and so formed articles". This invention is related to a process for producing a surface! ! layer with high wear resistance and decreased coefficient of ] friction. Said layer consists of manganese (Mn) comprising | oxygen (O) and nitrogen (N) or oxygen (0), sulphur (S) and nitrogen (N) and is applied on surfaces of articles of aluminum (Al) and aluminum alloys. Said layer exhibits a metallurgical bond (fusion bond) to the substrate, i.e. bonding to the substrate by diffusion caused by heating or optionally melting. Numerous efforts to improve the wear resistance of aluminum alloys by oxydizing, chromizing or iron coating said alloys by a galvanic treatment (anodic method) are previously known. ! Galvanic (electrolytic) layers characteristically are inferior! to heat bonded layers as regards adherence. Thus there is a \ need for forming galvanic (electrolytic) surface layers on j aluminum or aluminum alloy substrates with the same good | characteristics as heat bonded layers. ! Experiments performed with nitriding previously known galvanic layers of iron and chromium coated onto aluminum and aluminum alloy substrates have not given any useful results, e.g. because of peeling and chipping of the layer from the substrate. According to this invention it is possible to form surface layers with good wear resistance and low friction and simultaneously good adherence to a substrate of aluminum and ■aluminum alloys. For this purpose the invention uses a : coating based on manganese which is applied onto the surface of the substrate of aluminum or aluminum alloys, preferably by j galvanic or electrolytic coating. Methods for galvanic or i ;electrolytic coating of manganese onto aluminum and aluminum alloys are per se previously known. According to the inven¬ tion it is possible to obtain excellent adherence of such manganese coatings to the substrate of aluminum and aluminum alloys and simultaneously obtain the previously mentioned good characteristics as regards wear resistance and low friction. This is achieved according to the invention by heat treating the manganese coating and including oxygen and nitrogen or oxygen, sulphur and nitrogen in said coating. The heat treat¬ ment according to the invention is preferably performed at a temperature of from about 653 up to the melting point, prefer¬ ably up to 920°K, especially 753-883°K. Said heat treatment is preferably performed for a period of at least 0.5 hour and preferably up to 10 hours. The introduction of oxygen and nitrogen in the coating is preferably achieved by heat treating in an atmosphere which supplies nitrogen and oxygen to the manganese layer under the heat treating conditions, preferably an oxidizing treatment in an oxidizing atmosphere, preferably an atmosphere comprising water vapour, preferably for a period of at least 0.5 hours and preferably up to 1.5 hours, and a nitriding treatment, preferably in ammonia or cracked ammonia, preferably for a period of at least 0.5 hours and prefer-ably up to 6 hours. These oxidizing and nitriding treatments are preferably performed at a temperature of 753 to. 883°K and suitably simultaneously with the previously mentioned heat treatment for bonding the manganese .layer to the substrate. The introduction of oxygen, sulphur and ; nitrogen in the coating is preferably achieved by heat j treating in an atmosphere which supplies nitrogen, sulphur and' oxygen to the manganese layer under the heat treating conditions, preferably an atmosphere comprising ammonia (NH_) ! and sulphur dioxide (SO_). The introduction of oxygen, sulphur and nitrogen into the manganese layer is preferably performed simultaneously with the previously mentioned heat j treatment. Preferably ammonia and sulphur dioxide are supplied to the reaction in the gaseous state through separate conduits in order to facilitate and improve the control of the process. The quantity of SO„ added depends upon the size of the treated articles and is usually from 1.0 to a few per cent, e.g. up to 5% of the ammonia volume. With the process according to this invention it is possible to form on the surface of aluminum and aluminum alloy substrates a composite type coating layer which is characterized by high hardness and very good adherence to the substrate and a reduced coefficient of friction. The surface coating layer according to the invention comprises in addition to manganese also various compounds of manganese with nitrogen and oxygen, e.g. of the type Mn.N, Mn.,0., etc., as particulate precipitates in the manganese matrix, or various compounds of manganese with nitrogen, oxygen and sulphur, e.g. of the type Mn. (N, S, 0), in which the mutual quantity ratios of N, S and 0 may vary, i.e. from pure Mn,N, and, furthermore, compounds of the types Mn 2 (0,S),, Mn 3 (0,S) ., etc., as particulate precipitates in the manganese matrix. The maximum hardness in the layer is usually present at a certain distance from the surface, as is usual in nitriding processes, and may exceed HV 0.01 •= 900. The process according to the invention can basically be used for the treatment of all kinds of aluminum and aluminum alloy articles, e.g. parts for internal combustion engines, e.g. spark ignition and diesel engines, e.g. pistons and similar articles, engines with rotating piston, such as wankel engine ■ and in general for articles of aluminum and aluminum alloys which are subjected to wear and/or are intended to exhibit low friction. The aluminum alloy should preferably have a compo¬ sition which permits coating, especially electrolytical coating with manganese (or optionally with manganese alloys consisting mainly or to at least 75% or 90% of manganese) and ; firm bonding of the manganese (or manganese alloy) coating to ; the aluminum substrate by heat bonding (metallurgical bonding) . The invention is now illustrated with the following examples, j EXAMPLE 1 Substrate:aluminum articles which were degreased in a solution, of: H 2° 273 ml a 3 P0 4 13.5 g j NaOH 2.1 g Na 2 Si0 3 10.5 g Temperature 323°K for 5 minutes. The articles were then rinsed in hot and cold water and then dipped into a solution of: HCl 0.580 1 MnS0 4 .5H 2 0 7 g H 2 0 1.76 1 Said treatment was performed at a temperature of 310°K and for 15-30 seconds. After careful rinsing in water the aluminum articles were directly subjected to an electrolytic manganizing treatment (electrolytic manganese precipitation) in an electrolyte of the following composition: MnS0 4 .5H-,0 200 g/1 (NH 4 ) 2 S0 4 75 g/1 : H 2 0 to 1 litre Electrolyte temperature 283-288°K, electrolyte pH = 7.0 2 Current density 10-15 x 10 A/m 2 . The electrolytic manganizing process was performed with anodes made from an alloy of, by weight: Sn 30%, Co 0.4%, balance Pb. It is preferable to stir the electrolyte continuously and to use a diaphragm for dividing the anode from the cathode. Immediately after removal from said electrolyte the articles were immersed in a 5% aqueous solution of: Na 2 Cr 2 0 7 .2H 2 0. After said electrolytic manganizing the aluminum articles were subjected to an oxidizing treatment in water vapour for 0.5 hours and a nitriding treatment in ammonia for 2 hours, both at the temperature 813°K. EXAMPLE 2 The same substrates and pretreatment as in Example 1 were used but instead of the oxidizing-nitriding treatment of Example 1 the aluminum articles were subjected to a heat treatment for introducing oxygen (0), sulphur (S) and nitrogen (N). in an atmosphere comprising a nitrogen source (ammonia, NH.,), a sulphur source and an oxygen source (sulphur dioxide, S0 2 ) at a temperature of 883°K for 3 hours. EXAMPLE 3 Substrate:aluminum alloy articles with the following composition: Si = 12.4%, Cu = 0.9%, Mg = 1.3%, Ni = 0.9%, Fe - 0.3%, balance Al. The articles were degreased in the same kind of solution and in the same way as according to Example 1. The articles were ■ then rinsed in hot and cold water and thereafter immersed into ; a solution of: HN0 3 75% by volume , HF 25% by volume. !t ( I Said treatment was performed at a temperature of 293°K and for; f 15-30 seconds. Immediately thereafter the articles were j carefully rinsed in water and subjected to electrolytic j manganizing. The composition of the electrolyte and the treatment conditions were the same as in Example 1. After said electrolytic manganizing the aluminum alloy articles were subjected to an oxidizing treatment in water vapour for 1.5 hours and a nitriding treatment in ammonia (cracked ammonia) for 6 hours, both at a temperature of 753°K. IThe prepared coatings comprise Mn and hard Mn-,0 4 and Mn 4 particles. The surface hardness after said oxidizing and " nitriding treatments may exceed HV 0.01 = 1000. EXAMPLE 4 The same substrates and pretreatments as in Example 3 were used but instead of the oxidizing and nitriding treatments of Example 3 the aluminum alloy articles were subjected to a heat, treatment in an atmosphere comprising an oxygen source, a sulphur source and a nitrogen source for simultaneous intro¬ duction of said elements into the layer, said atmosphere comprising ammonia (NH-,) and sulphur dioxide (SO-) at a temperature of 753°K for 10 hours. Said treatment can be regarded as an oxygen, sulphur and nitrogen saturation treatment. ____, Among articles subjected to the treatments according to the examples were combustion engine pistons and cylinder blocks. The manganese coating according to this invention preferably comprises the compounds or reaction products of manganese with oxygen, nitrogen and optionally sulphur embedded as particles ' in a matrix of manganese metal or alloy, especially as a composite coating. The amount of oxygen, nitrogen and optionally sulphur in the coating preferably is an amount corresponding at least to the amount introduced by heat treatment in water vapor or ammonia (or cracked ammoni^) or a mixture of ammonia and sulphur dioxide for 0,5 hours at 753°K. The manganese coating thickness should be sufficient to give good bonding to the substrate and to form or comprise reaction products of manganese with oxygen and nitrogen or with oxygen, nitrogen and sulfur resp. A suitable thickness may be e.g. at least 0,1 micron, preferably at least 0,5 micron , at least 1 micron or at least 5 microns , optionally at least 10 microns, or at least 50 microns. A suitable upper thickness limit may be e.g. up to mm, up to 1 mm or up to 0,5 mm or optionally up to 0,1 mm. Also a coating thickness outside said ranges may be used The manganese coating may optionally be applied also by e.g. electroless coating, flame spraying or plasma flame spraying deposition from a vapour phase, such as a manganese compound vapor phase , e.g. metallizing with manganese, e.t.c. Optionally the reaction products with oxygen, nitrogen and optionally sulfur may be included into the manganese coating already in the coating step, e.g. as reaction products formed already prior to the coating step or in the coating step. The coating may comprise also other constituents, such as conventional impurities normally present in the raw materials or deliberately added constituents which do not prevent or substantially reduce the desired inventive effect. Preferably the compsition of the substrate and of the coating are selected so that the coefficient of linear (thermal) expansion match, preferably with a difference in relation to the the aluminum or aluminum alloy substrate of at most 50$, optionally at most 25 % or at most 10.. or even at most 5% within the temperature range of intended use of the coated product.

Claims: CLAIMS 1. A process for forming a surface layer on aluminum and aluminum alloy articles, characterized by forminng on the surface of the article a coating comprising manganese and reaction products of manganese with oxygen and nitrogen or with oxygen, nitrogen and sulphur. 2. A process according to claim 1 characterized by coating the surface of the article with a manganese layer and heating the coated article in a gas atmosphere or gas atmospheres which supplies-oxygen, nitrogen and optionally sulphur to the manganese layer. 3. A process according to claim 1 or 2, characterized in that said heating for supplying oxygen, nitrogen and optionally sulphur is performed for at least 0,5 hour at a teenmperature of at least 753 K and preferably up to 883°K. -4. A process according to any of the preceding claims, characterized in that oxygen is supplied by an oxidizing treatment in a water vapour containing atmosphere, preferably for from 0,5 to 1,5 hours, and nitrogen is supplied by a nitriding treatment in an atmosphere comprising ammonia or cracked ammonia, preferably for from 0,5 to β hours; or oxygen, nitrogen and sulphur are supplied by a heat treatment in an atmosphere comprising ammonia and sulphur dioxide for from 0,5 to 10 hours. 5- A process according to any of the preceding claims, characterized in that the manganese coating is applied to the article with an electrolytic method. o . A process according to any of the preceding claims, characterized in that said heat treatment is performed so that the manganese layer through said heat treatment is structur¬ ally or metallurgically bonded or united to the aluminum or aluminum alloy substrate. 7. An article comprising at least a surface part of aluminum or aluminum alloy, characterized in that the aluminum or aluminum alloy surface is provided with a surface coating comprising manganese and reaction products of manganese with oxygen and nitrogen, -or with oxygen,nitrogen and sulphur, preferably as particles dispersed in a manganese surface layer matrix. 8. An article according to claim η , characterized by consisting of an article which is intended to be subjected to or resistant to heating and/or wear, such as internal combustion engines, e.g. spark ignited and diesel engines. 9- ^ An article according to claim 7 or 8 > characterized in that said manganese layer is by heat treatment diffusion or melt bonded and/or metallurgically bonded to the aluminum or aluminum alloy substrate and/or comprises compounds or reaction products of manganese with nitrogen and oxygen or with oxygen, nitrogen and sulphur

Inventors: SERBINSKI ALFRED, SERBINSKI WALDEMAR, SERBINSKI, ALFRED, SERBINSKI, WALDEMAR
Applicants: SERBINSKI ALFRED, SERBINSKI WALDEMAR, SERBINSKI, ALFRED, SERBINSKI, WALDEMAR
Application year: 1985
Main classification: C23C8
IPC codes: C23C8, C23C26, C25D3, C25D5