PRE-TREATMENT METHOD FOR METAL ALLOYS

FIELD OF INVENTION

[0001] The present invention relates to a method of pre-treatment for metal alloys and more particularly to a method of pre-treatment for magnesium alloyed die cast products, which enhances the corrosion resistance and adhesive bonding of the said products, thereby making it ideal for use in automotive applications.

BACKGROUND OF INVENTION

[0002] Magnesium alloys provide excellent mechanical and physical properties, such as low density, high strength-to-weight ratio, good heat and electrical conductivity, good electromagnetic wave-screening ability, and good damping properties. In comparison to steels or aluminum based alloys, magnesium alloys provide many superior properties, particularly with respect to low density and high strength-to-weight ratio, which makes magnesium alloys attractive for applications where weight reduction is critical including applications in aerospace, automotive, transportation, electronic devices and hand tools. For instance, the use of magnesium alloys in forming automobile parts has experienced rapid growth in recent years because of the demand for more light weight and fuel efficient vehicles. Magnesium alloys also offer other advantages including superior castability and machinability properties.
 
[0003] Magnesium alloyed die cast products, however, are very vulnerable to corrosion due to the reactive nature of magnesium. Products alloyed from magnesium alloys, used in automotive applications, are generally subjected to corrosion resistance treatment. Such products are required to have high corrosion resistance due to probable exposure to temperature extremes, water, snow, ice and humidity, as well as corrosion inducing materials such as salt, dirt and road grime that can retain moisture and salt. A commonly used, low cost, corrosion resistant treatment for magnesium alloyed die cast products is a dichromate-based conversion coating. While dichromate based conversion coatings provide good corrosion protection, they are based on a chemical compound (hexavalent chromium), which is highly toxic and is a known carcinogen.

[0004] It would therefore be very beneficial to have a pretreatment method for die cast products alloyed from magnesium alloys, which enhances the corrosion resistance and adhesion bonding of the product and this forms the primary objective of the present invention. It is another objective of the present invention to provide a pretreatment method, which is non-toxic and environment friendly. It is yet another objective of the present invention to provide a pretreatment method, which makes the magnesium alloyed die cast product ideal for use in automotive applications.

SUMMARY OF THE INVENTION

The current invention discloses a pretreatment method of alloys using non-toxic and environment friendly pretreatment method for die cast products alloyed from magnesium alloys, which enhance the corrosion resistance and adhesion bonding of the product. The present invention provides a pretreatment method, which makes the magnesium alloyed die cast product ideal for use in automotive applications. The present pretreatment method thus involves step of degreasing the magnesium alloyed die cast product in degreasing solution, a repetitive rinsing in a rinsing solution, treating the magnesium alloyed die cast product surface with an acidic solution and then again rinsing the die cast before treating in oven for drying.

BRIEF DESCRIPTION OF DRAWINGS

[0005] Figure 1 Shows a typical scooter type two-wheeler.

[0006] Figure 2 Shows a vehicle with essential embodiments of the invention.

[0007] Figure 3 Illustrates an utility box and the provision for slot therein.

[0008] Figure 4 Illustrates an utility box of a typical scooter type two-wheeler.

[0009] Figure 5 Illustrates the guide path for fuse housing.

DETAILED DESCRIPTION OF THE INVENTION

[00010] The pre-treatment method for magnesium alloyed die cast products as per the present invention comprises the following steps namely degreasing the product, rinsing the product with a first cleaning solution and thereafter with a second cleaning solution, chemical treating of the product, rinsing the product with a third cleaning solution and oven heating of the product. The steps are performed in the above-mentioned sequence.

[00011] Degreasing is conducted in order to remove contaminants such as oil, grease, dust, iron powder and the like. In the present invention, degreasing is done using an alkaline solution at a temperature of about 50° C for time duration of about 120 seconds. The degreased magnesium alloyed die cast product is then rinsed with a first cleaning solution and further rinsed with a second cleaning solution. The first cleaning solution is preferably water and the second cleaning solution is preferably de-ionized water. The water rinses are conducted to clean the product surface after degreasing and to avoid possible contamination of the consequent bath. The rinsed product is then treated with a trivalent chromium chemical based acidic aqueous solution. The acidic aqueous solution has about 10% concentration of trivalent chromium chemical and is maintained in a ph range of 3.5 to 3.9. This step is conducted in room temperature for time duration of about 90 seconds. The treated product is then rinsed with a third cleaning solution, which is preferably de-ionized water. The product is thereafter dried in an oven in a temperature of about 80° C for time duration of about 600 seconds. The pre-treatment method as per the present invention, results in a protective chromate coating of thickness in the range about 50-500mg/m2.

[00012] The magnesium alloyed die cast product pretreated according to the above method, was then powder coated by spraying polyester based powders and baked in a temperature range of about 60° C to 80° C, and was further subjected to performance tests. Specimens of pretreated product after powder coating and baking were made to undergo neutral salt spray test and wet adhesion test. The specimens were cross hatch scribed prior to exposure to boiling water. Paint adhesion loss along scribe lines was determined by a tape pull test. The results of the performance tests are tabulated below:-

[00013] Die cast products alloyed from magnesium alloy AZ91D, when pretreated by the method according to the present invention, displayed much enhanced corrosion resistance and adhesive bonding. The die cast products pretreated as per the present invention is thus ideal to be used in automotive applications such as clutch covers, magneto cover, cylinder head cover etc. Further, trivalent chromium is non toxic and non hazardous therefore making the present invention environment friendly.

[00014] The foregoing description is a specific embodiment of the present invention and has been described for the purpose of illustration only. Persons skilled in the art may practice numerous alterations and modifications of the present invention without departing from its spirit and scope.

We Claim:

1. A method of pre-treating a magnesium alloyed die cast product, said method comprising the steps of:

a) degreasing the magnesium alloyed die cast product with a degreasing solution;

b) rinsing the magnesium alloyed die cast product surface degreased in step(a) with a first cleaning solution;

c) rinsing the water rinsed magnesium alloyed die cast product surface of step (b) with a second cleaning solution;

d) treating the magnesium alloyed die cast product surface of step(c) with an acidic aqueous solution comprising per liter of solution about lOOgrams of a trivalent chromium chemical, said acidic aqueous solution having a ph ranging from about 3.5-3.9;

e) rinsing the treated magnesium alloyed die cast product surface of step (d) with a third cleaning solution; and

f) oven drying the rinsed magnesium alloyed die cast product surface of step(e).

2. The method of pre-treating a magnesium alloyed die cast product as claimed in claim 1, wherein said magnesium alloy is preferably AZ91D and the said magnesium alloyed die cast product is preferably a clutch cover.

3. The method of pre-treating a magnesium alloyed die cast product as claimed in claim 1, wherein step (c) is conducted at room temperature for a time duration of about 90 seconds.

4. The method of pre-treating a magnesium alloyed die cast product as claimed in claim 1, wherein step (f) is conducted at about 80° C for time duration of about 600 seconds.

5. The method of pre-treating a magnesium .alloyed die cast product as claimed in claim 1, wherein step (a) is conducted at about 50° C for time duration of about 120 seconds and the degreasing solution used is an alkaline solution.

6. The method of pre-treating a magnesium alloyed die cast product as claimed in claim 1, wherein the first cleaning solution in step (b) is water.

7. The method of pre-treating a magnesium alloyed die cast product as claimed in claim 1, wherein the second cleaning solution and third cleaning solution in step (c) and step (d) respectively is de-ionized water.

8. The method of pre-treating magnesium alloyed die cast product as claimed in claim 1, wherein said method results in a protective chromate coating in the range about 50-500mg/m2.

9. The method of pre-treating magnesium alloyed die cast product as hereinabove described in the specification.