US3418174A

US3418174A - Method of making gal vannealed ferrous metal of improved solderability

Info

Publication number: US3418174A
Application number: US390998A
Authority: US
Inventors: Paul R Carter; Lawrence E Helwig
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1964-08-20
Filing date: 1964-08-20
Publication date: 1968-12-24
Anticipated expiration: 1985-12-24

Description

United States Patent 3,418,174 METHOD OF MAKING GALVANNEALED FER- ROUS METAL OF IMPROVED SOLDERABILITY Paul R. Carter, Monroevilie Borough, and Lawrence E.

Helwig, Hampton Township, Allegheny County, Pa., assignors to United States Steel Corporation, a corporation of Delaware No Drawing. Filed Aug. 20, 1964, Ser. No. 390,998

2 Claims. (Cl. 1486.35)

ABSTRACT OF THE DISCLOSURE A process for producing galvannealed ferrous metal of improved solderability is disclosed. A ferrous metal base is galvanized with zinc which contains aluminum. The coated base is galvannealed by heating to substantially completely alloy the coating with the ferrous metal. The galvannealed material is treated with steam, preferably under pressure, to improve the solderability thereof.

This invention relates to a method of improving the solderability of galvannealed ferrous metal. The terms ferrous and ferrous metal, as used herein, refer to iron and iron alloys.

Galvannealed ferrous metal articles such as sheet or strip are produced by passing galvanized, i.e. zinc coated, ferrous metal through a heating zone that maintains the coating molten until it alloys substantially completely with the ferrous base. Galvannealed coatings possess a silvery matte finish of relatively low reflectivity and have good paint adherence properties. However, the solderability of galvannealed ferrous metal is very poor and precludes the use of the material where good solderability is required. It is currently thought that aluminum contained in the zinc used to coat the ferrous metal during galvanizing before annealing is responsible for the poor solderability of galvannealed articles. Aluminum oxides readily and the oxide film, which may be a mixture including aluminum oxide, appearing at the coating surface is nearly impervious to solder fluxes and makes soldering extremely difficult. As much as from about 0.007 to 0.25% aluminum may be present in the zinc metal used for coating. Although aluminum-free galvanized coatings could be used to make galvannealed articles of improved solderability, this approach is not commercially practical because a small amount of aluminum is desirable in galvanized coatings and the same production lines are used for galvannealing as are employed to produce galvanized material.

Several methods of removing the undesirable surface oxide from galvannealed metal surfaces have been proposed, but most are objectionable because they either interfere with paint adhesion or are difiicult to control. One such method involves treating the oxide surface with mineral acids to dissolve the oxide; however, this technique tends to remove too much coating along with the oxide and further requires extensive rinsing. Alkali treatments also remove the oxide but present difiiculties in subsequent painting operations because even small 3,418,174 Patented Dec. 24, 1968 Iceamounts of residual alkali on the surface would be likely to interfere with paint adhesion.

The present invention provides a method of producing galvannealed ferrous metal with improved solderability from material galvanized with zinc which contains some aluminum. According to the invention, galvanized ferrous metal which has been coated with aluminum-containing zinc is galvannealed by heating to substantially completely alloy the coating with the base, aluminum oxide being formed at the coating surface, and the galvannealed ferrous metal is contacted, e.g. by dipping, spraying, etc. with water at a temperature of at least 80 C. Still greater improvements in solderability can be obtained by using boiling water or steam. With relatively short treating times of up to about 10 minutes the degree of solderability improvement is proportional to the length of time the galvannealed ferrous metal is subjected to the treatment. Although the precise explanation of how the solderability is improved is not fully understood, it is believed that the improvement results from hydration of the oxide film.

solderability can be evaluated by means of a test that measures the solder flow of a standard size solder pellet. As the solder spot is melted on a hot plate, 61g. at 525 F., the pellet will either flow or bead depending upon the flow properties of the sheet surface. Good flow properties will cause the melted solder pellet to spread over a large area with the result that the thickness of the solder spot (measured with a micrometer) is reduced accordingly. Hence low solder spot thicknesses indicate good solderability.

The following examples illustrate various embodiments of the invention:

Example I Two different samples of galvannealed sheet produced by a continuous strip operation were immersed for various times (0 to 20 minutes) in water at 80 C., 90 C. and 100 C. At each temperature, the longer the specimens were immersed the better were the solder-flow properties, as the following Tables I and II indicate. The specimens also gained weight in water which indicates that a chemical reaction had occurred. Boiling water (100 C.) was found to be much more effective than water at lower temperatures, where the improvement was sporadic. At 100 C. maximum improvement resulted in about 10 minutes.

TABLE I.EFFECT OF PRETREATMENT IN HOT WATER gg s mDER-FLOW PROPERTIES OF GALVANNEALED Sample No. 1

Boiling Water, Hot Water, Time in Water, mm. 100 C. 80 C.

Wt. Gain, Solder Wt. Gain, Solder mgJdm/ Ht, mils mgJdm. Ht. mils 0 96 0 96 0. 04 71 0. 14 85 0. 18 0. 22 67 0.26 26 0. 32 70 0. 41 13 0.32 73 NT NT 0. 57 66 0. 60 15 0. 96 83 O. 11 NT NT 1. 42 13 NT NT 3. 10 NT NI NoTE.-N1=No test conducted.

FLOW PROPERTIES OF GALVANNEALED SHE Sample No. 2

Boiling Water, Hot Water, Hot Water, Time in water, min. 100 C. 90 C. 80 C.

Wt. Gain, Solder Wt. Gain, Solder Wt. Gain, Solder mgJdm. Ht., mgJdnL Ht., mgJdm. Ht., mils mils mils 78 0 78 0 78 NT NT 0.41 56 0. 10 49 0.10 56 0.35 46 0. 39 54 0. 23 43 NT NT 0. 38 37 0. 41 44 0. 51 46 0.89 41 0. 69 36 NT NT 0.86 26 0. 46 29 0.89 38 1.05 28 0.69 26 NT NT 1. 31 20 0.82 29 1. 53 29 1. 69 33 0. 9T 20 NT NT NT NT 1. 38 52 2. 16 38 2.84 23 2. 24 15 3. 16 29 3. 41 18 NOTE.-NT=N0 test conducted.

Example II can be improved considerably with hot water, i.e., 80

Specimens of galvannealed sheets were placed in a pressure vessel and held at various steam pressures (0 to 15 p.s.i.) for various lengths of time (0 to 10 minutes). The improvement in solder-flow-test performance, as reported in Table III, was greater when the specimens were kept in contact with steam for longer periods, or when higher pressures were used. Maximum improvement occurred in about 10 minutes, at 0 p.s.i., minutes at 5 psi, 3 /2 minutes at psi, and 1 /2 minutes at psi. (The last figure is estimated, since all specimens treated at 15 psi. had reached the maximum solder improvement in the time it took to close the pressure vessel, to bring it up to 15 p.s.i., release the pressure, and remove the specimens.) The higher the steam pressure and therefore the hotter the steam, the shorter was the time required to reach maximum improvement in solderability.

TABLE III.EFFECT OF STEAM ON SOLDIER-FLOW PROPERTIES [Sample No. 2]

1 Total times include the time to reach the indicated pressure, the 5 5 time at pressure, and the time to exhaust steam to open vessel.

3 Control, no pretreatment.

C. or higher and solderability can be improved still further by treatments in boiling water. Shorter time periods can be used to obtain equivalent improvement when the galvannealed material is subjected to steam under pressure.

While we have shown and described only a single embodiment of our invention, it is apparent that modifications may arise. Therefore, we do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

We claim:

1. A process for producing galvannealed ferrous metal of improved solderability comprising galvanizing a ferrous metal base with metallic zinc which contains aluminum to provide a coating on the ferrous metal, galvannealing said zinc-coated base by heating to substantially completely alloy said coating with said ferrous metal and contacting said galvannealed ferrous metal with steam to improve the solderabilty thereof.

2. A process according to claim 1 wherein said steam is under pressure.

References Cited UNITED STATES PATENTS 287,076 10/1883 Young 1l7l02 2,884,350 4/1959 Saubestre 148-614 3,177,088 4/1965 Sievert 1171 14 X 3,247,026 4/ 1966 Switzer 1486.27

OTHER REFERENCES Galvanizing Techniques In the .U.S.A., O.E.E.C. Report by a group of European experts, published by the Organization for European Economic Cooperation, Paris, 1953, pp. 36 and 37 relied on.

ALFRED L. LEAVITT, Primary Examiner.

U.S. Cl. X.R.