JPH0543776B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is for use in parts of vehicles, electrical equipment, etc. that are cast into a mold, surfaced at desired locations to give a metallic luster, and coated with a transparent film on that location. This invention relates to an aluminum alloy with excellent filiform corrosion resistance. (Prior Art) It is well known that the properties of aluminum, such as strength, corrosion resistance, and fluidity, can be improved by selecting the elements to be added to aluminum and alloyed with it. Among these, Si has a remarkable improvement in strength and fluidity compared to aluminum, so Al-Si alloys made by adding Si to aluminum are widely used. In particular, with Al-Si alloys, when the alloy is cast into a mold and rapidly solidified, Si crystallizes finely.
It forms a eutectic structure with Al and can improve not only strength but also wear resistance, so many of the parts that require these characteristics, such as vehicle wheels and other electrical equipment parts such as VTRs, are cast in molds. Manufactured by The casting methods used for molds include die casting, low pressure casting, gravity casting, etc., which are selected based on product quality, productivity, etc., and are known as general methods. . Incidentally, the metallic luster of aluminum is beautiful and gives it a sense of fashion, and for this purpose it is used by cutting the desired position of a cast product to expose the metal base, but it is easily corroded by moisture and environmental pollution. For this reason, the exposed metal surface is treated with chemical conversion treatment, alumite treatment, or coated with clear resin. (Problem to be solved by the invention) A product in which the surface of the exposed metal base is alumite treated with a film thickness of 7-9 μm to provide corrosion resistance exhibits a color characteristic of the product's alloy components, and is difficult to impart the metallic luster of aluminum. , especially Si in 4-
Al-Si alloys containing 5 wt% or more exhibit a gray to black-gray color and no longer have the metallic luster of aluminum. In addition, products that have been chemically treated or coated with clear resin on a metal base surface may have uneven film thickness depending on the shape of the product. unable to
It is easy to corrode from that part, and from scratches received during use. Therefore, it may be considered to make the film even thicker, but this would have the opposite effect. In other words, films formed by chemical conversion treatment or painting are dried to remove the moisture and organic solvents they contain, but the thicker the film, the more likely it is that microscopic cracks will occur.
This part becomes susceptible to corrosion. However, the thin and desirable thickness of the film allows moisture to easily penetrate.
The small amount of water that penetrates reacts with the base aluminum and corrodes it, causing so-called filiform corrosion that grows in a curved manner over time, and sometimes 44% in a few months.
-5 mm, and the density of the points where they occur is large, which poses a problem that makes it hard to damage the appearance. The present invention has solved these problems, and its purpose is to provide a gold-based casting aluminum alloy in which filamentous corrosion occurs at a low density and at a slow rate of occurrence. . (Means for Solving the Problems) As a result of repeated research to solve the above problems, the inventors found that if the Cu content of the alloy is kept as small as possible, the density of filiform corrosion occurrence points is small, and the alloy The present invention was completed by discovering that when one or both of Ti and Be are contained in a steel, the rate of progress of filamentous corrosion growth is slowed down. That is, in the first invention, the content of Cu is
In aluminum alloys that are regulated to 0.02wt% or less and contain 4-13wt% Si, 0.05-0.3wt
It is an aluminum alloy for mold casting that is used with a transparent film and has excellent thread corrosion resistance, and is characterized by containing one or two types of % Ti and 0.05-0.15 wt% Be. , and the second invention regulates the Cu content to 0.02wt% or less, and
Contains Si4−13wt%, Mg1.5wt% or less, Mn1.2wt% or less, Fe1.5wt% or less, and further contains 0.05−
It has excellent filamentous corrosion resistance and is used with a transparent film containing 0.3wt% Ti and 0.05-0.15wt% Be, with the remainder being Al and other impurities. The third invention is an aluminum alloy for mold casting, in which the Cu content is regulated to 0.02wt% or less, and the Si6-8wt
%, Mg1.5wt% or less, Mn0.3wt% or less, Fe0.3wt
% or less, and further contains 0.05-0.3wt% of Ti and 0.05-0.15wt% of one or both of Be, with the balance consisting of Al and impurities other than the above. It is an aluminum alloy for mold casting by gravity or low-pressure casting method, which has excellent thread corrosion resistance.
The invention regulates the Cu content to 0.02wt% or less,
and Si8−11wt%, Mg0.15−0.5wt%, Mn0.1−
Contains 0.5wt%, Fe0.3−0.8wt%, and further 0.05
A filamentous corrosion resistant film that is used with a transparent film containing one or two of -0.3wt% Ti and 0.05-0.15wt% Be, with the remainder being Al and other impurities. It is an excellent aluminum alloy for die casting. (Function) Al-Si alloys containing 4-13wt% Si have good fluidity and good filling properties, and are used in vehicle wheels,
It is suitable for casting parts of electrical equipment such as VTRs. The preferred Si content is 6-11 wt%.
Especially when gravity or low-pressure casting methods with slow cooling rates are used, primary Si and eutectic Si tend to coarsen, reducing toughness or wear resistance, so the Si content is preferably 6-8 wt%. . Also, when using the die-casting method, the cooling rate is fast,
Since there is little effect of deterioration of properties due to coarsening of primary crystal and eutectic Si as mentioned above, its content is 8-
The content is preferably 11 wt%. Cu 0.02wt% or less Cu increases the density of filamentous corrosion points, so it is preferable to keep its content as small as possible, preferably 0.02wt% or less.
It should be 0.01wt% or less. This is because by containing Cu, a second phase of α-Al(Fe, Cu)Si containing Cu is crystallized, and this second phase becomes more noble with respect to the matrix, forming a local battery. This is thought to be the starting point for filamentous corrosion. One or two types of Ti0.05-0.3wt% Be0.05-0.15wt% The purpose of containing one or both of Ti and Bi is to suppress the growth rate of filamentous corrosion that has occurred. If the content is less than 0.05wt% for Ti and less than 0.05wt% for Be, the suppression effect will be small;
Moreover, when the content of Ti exceeds the upper limit value, coarse Al-Ti-based compounds tend to crystallize, which shortens the life of the cutting tool and reduces its toughness.
In addition, when the Be content exceeds the upper limit,
This is undesirable because Be oxide pollutes the atmosphere in the workplace during alloy melting. Although it is not precisely known why the inclusion of one or both of Ti and Be slows down filamentous corrosion growth, it is possible that Ti or Be acts on factors that increase the oxygen overvoltage, for example. , the cathodic reaction (O ₂
+H ₂ O+4e→4OH ^- ), the rate of the reaction is significantly suppressed, and as a result, the rate of progress of corrosion is slowed down. Here, the Al-Si alloy containing 4-13wt% Si does not mean limited to Al-Si alloy, but in addition to Ti and Be in the above content range,
Elements such as Mg, Mn, Fe, etc. may be contained, and if it is desired to further impart strength, toughness, mold seizure resistance, etc., alloying elements can be added depending on the purpose, The amount is not particularly limited, but for example, in addition to the 4 types of JIS H5202 aluminum alloy castings and the 3 types of JIS H5302 aluminum alloy die castings, as well as commercially available alloy castings, Mg is set at 0.15-1.5wt%. , 1.2wt% or less of Mn, and 1.5wt% or less of Fe. Especially when gravity or low-pressure casting is used, Mn and Fe tend to crystallize coarse Al-Mn-Fe compounds, which impairs strength and toughness, so Mn should be 0.3 wt% or less and Fe 0.3 wt% or less. is preferred. In addition, when using the die casting method, Mn or Fe is used to provide mold seizure resistance.
It is necessary to contain one or two types of Mn, and the amount thereof is 1.2 wt% or less in terms of Mn, preferably 0.1-
0.5wt%, less than 1.5wt% Fe, preferably Fe0.3−
It is 0.8wt%. In addition to the elements mentioned above, Cr, W, Ni
Zn content of up to about 0.5 wt%, up to about 1 wt% of Zn, preferably up to 0.5 wt%, is permissible because it does not impede the effects of the alloy of the present invention. When producing the alloy according to the present invention, Si is metallic silicon or an Al-Si master alloy, Ti is an Al-Ti master alloy or a flux containing a Ti compound such as _KTiF5 , and Be is an Al-Be A master alloy etc. is added to the molten aluminum and stirred to be incorporated therein. The molten aluminum is a metal with a purity of 3 or more types, preferably 1 or more types according to JIS H2102 aluminum metal,
Control the Cu content by diluting the amount of Cu that tends to be contained in returned materials. The molten aluminum alloy produced in this manner is cast into a mold. This method rapidly cools the molten alloy to form a fine eutectic Si structure, improving properties such as strength and toughness, and creating an α-Al(Fe.M)Si compound (M is
This is to suppress the crystallization of the second phase of metals other than Al, Fe, and Si, and to reduce the density of filamentous corrosion points. As mentioned above, gravity casting, low pressure casting, die casting, etc. can be used for this mold casting. The castings cast in this way are subjected to plastic processing such as heat treatment and forging as necessary, and then cut at desired locations to give the aluminum a metallic luster, and undergo chemical conversion treatments such as chromate treatment and transparent resin. ,
It is made into a product by applying a coating such as paint or enamel.
Alumite treatment does not produce a grayish color to the extent that it interferes with the metallic luster of aluminum if the thickness is up to about 1 μm, so it is inconvenient to provide this level of alumite film on the metal surface of the casting after cutting. This is not a problem, but rather, it is preferable because it improves the adhesion with coatings such as resins as well as other chemical conversion coatings. Next, the present invention will be explained in more detail based on Examples. Since it has been confirmed that low-pressure cast products and gravity products have equivalent effects, die-cast products and low-pressure cast products will be explained in Examples. (Example) A test piece (100 mm x 250 mm x 10 mm thickness) was cast using a 250t die-casting machine and a 300Kg low-pressure casting machine. The molten metal used is a metal with a composition shown in JIS H2102 Aluminum Bullion Type 1, and this includes Al-Si, Al-Si,
Al−Mg, Al−Fe, Al−Mn, Al−Ti, Al−Be
Each master alloy was melted, degassed, and sludge removed. In the case of die casting, Fe,
Mn was added. Furthermore, Mg was added to give the alloy mechanical properties suitable for use in vehicle wheels. The analytical values are shown in Table 1. The mechanical properties and filamentous corrosion resistance of the test pieces thus obtained were measured. The results are shown in Table 2. Filiform corrosion resistance was investigated by accelerated corrosion test.
In other words, the test piece was surface-ground by 2 mm to make the aluminum metallic luster surface, degreased, and then chromate-treated.
A chemical conversion film containing mg/m ² of Cr was formed on the cut surface, and a commercially available acrylic urethane paint PG60 (manufactured by Kansai Paint Co., Ltd.) was applied to the sample. After drying, the film thickness of the paint was measured and found to be 20 μm. Next, a cross cut was placed in the sample, and the area was coated with 0.5N hydrochloric acid solution to cause rust to develop from this area, and then left in an atmosphere at a temperature of 40°C and a relative humidity of 80% for 10 days, causing filamentous corrosion. The density and maximum length of the point of origin were measured. Here, the density of the corrosion point is 0.5
Corrosion that grew to a length of mm or more was expressed as the number per 5 cm of the crosscut length.

【table】

[Table] From the results in Table 2, it can be seen that alloys with low Cu content (sample numbers 5 and 11) have a lower density of corrosion points than alloys with high copper content (sample numbers 6 and 12). . Alloys containing one or both of Ti and Be in addition to this alloy with a low Cu content (alloys of the present invention: sample numbers 1, 2,
3, 4 and 7, 8, 9, 10) have a shorter maximum corrosion length than the alloys with only a small Cu content (sample numbers 5 and 11). (Effects of the Invention) As described above, in the alloy of the present invention, the density of filamentous corrosion points is low and the maximum length of corrosion is short, so the cut surface of the product becomes dirty due to rust and the appearance becomes difficult to see. Since it retains its metallic luster without any scratches, it can maintain the fashionability and surface performance of vehicle wheels, audio parts, various mirrors, etc. over a long period of time.

Claims (1)

[Claims] 1. The content of Cu is regulated to 0.02wt% or less, and
In aluminum alloys containing 4-13 wt% Si, 0.05-0.3 wt% Ti and 0.05-0.15 wt%
An aluminum alloy for mold casting, which is used with a transparent film and has excellent thread corrosion resistance, and is characterized by containing one or two types of Be. 2 Regulate the Cu content to 0.02wt% or less, and
Contains Si4−13wt%, Mg1.5wt% or less, Mn1.2wt% or less, Fe1.5wt% or less, and further contains 0.05−
It has excellent filamentous corrosion resistance and is used with a transparent film containing 0.3wt% Ti and 0.05-0.15wt% Be, with the remainder being Al and other impurities. Aluminum alloy for mold casting. 3 The Cu content is regulated to 0.02wt% or less, and
Contains Si6-8wt%, Mg0.15-1.5wt%, Mn0.3wt% or less, Fe0.3wt% or less, and further contains 0.05-0.3wt%
% Ti and 0.05-0.15wt% Be of one or two types, with the balance consisting of Al and impurities other than the above. Gravity is used with a transparent film that has excellent filamentous corrosion resistance. Or aluminum alloy for mold casting using low pressure casting method. 4 Regulate the Cu content to 0.02wt% or less, and
Si8−11wt%, Mg0.15−0.5wt%, Mn0.1−0.5wt
%, Fe0.3−0.8wt%, and further 0.05−
It has excellent filamentous corrosion resistance and is used with a transparent film containing 0.3wt% Ti and 0.05-0.15wt% Be, with the remainder being Al and other impurities. Aluminum alloy for die casting.