target plates were prepared by combining the following three types of metals : aluminum alloy plate : al - mg alloy ( aluminum alloy plate was partially subjected to double action sanding with abrasive of grid80 , and ground ). such target plates were washed with an alkaline degreasing agent which was mainly composed of sodium phosphate so that the metal material surfaces were cleaned , then rinsed with water , and surface conditioned with aqueous titanium salt . then , the target plates were phosphated under treatment conditions described below , rinsed with water and pure water , and thereafter subjected to cation electrodeposition , intermediate coating and overcoating , for evaluation of after - coating performance . the target plates were dipped in a 2 . 0 wt . % aqueous solution of an alkaline degreasing agent ( surfcleaner sd270to by nippon paint co ., ltd .) at 40 ° c . for 2 minutes , to be degreased . the target plates were spray - washed with service water at the room temperature for 30 seconds . the target plates were dipped in a 0 . 1 wt . % aqueous solution of a surface conditioning agent ( surffine 5mz by nippon paint co ., ltd .) at the room temperature for 15 seconds . the target plates were dipped in treatment solutions having compositions shown in tables 1 to 3 for 2 minutes . tables 1 and 2 show inventive examples , and table 3 shows comparative examples . comparative example a had a small content of free f ions , comparative example b had a large content of free f ions , comparative example c had high free acidity , comparative example d had low free acidity , comparative example e had small contents of mn ions and ni ions , comparative example f had a large content of zn ions , and comparative example g had a small content of zn ions . comparative example d had a small content of zn ions , since the zn ions were not stably held in the bath due to the low free acidity . the target plates were spray - washed with service water at the room temperature for 30 seconds . the target plates were dipped in deionized water at the room temperature for 15 seconds . the target plates were coated with a cationic electrocoating paint ( oto - u - 2602 by nippon paint co ., ltd .) to obtain coatings of 25 μm in film thickness , which in turn were baked at 160 ° c . for 20 minutes . the target plates were spray - coated with a melamine - alkyd intermediate coating paint ( orga to 4830 by nippon paint co ., ltd .) and baked at 140 ° c . for 25 minutes , to obtain coatings of 35 μm in film thickness . the target plates were spray - coated with a melamine - alkyd top coating paint ( orga to 640 by nippon paint co ., ltd .) and baked at 140 ° c . for 25 minutes , to obtain coatings of 35 μm in film thickness . the target plates which were phosphated and coated under the aforementioned conditions were subjected to measurement of coating weights , an adhesion test , a filiform corrosion test , a salt spray test , and a composite corrosion cycle test , for evaluation of the coating surfaces . tables 1 to 3 shows the results . the evaluation was made on the aluminum alloy surfaces ( al materials ( including ground surfaces )), the steel surfaces ( fe materials ) and the galvanized steel surfaces ( zn materials ). the target plates were dipped in deionezed water of 50 ° c . for 10 days , and thereafter cut into the form of grids having 100 pieces at intervals of 2 mm with a sharp cutter . adhesive tapes were brought into pressure contact with the grid surfaces and then separated perpendicularly to the surfaces , for measuring the rates (%) of the pieces remaining on the plates . the target plates on which cutting was given to a salt spray test ( jis - z - 2371 ) for 24 hours , and thereafter subjected to a humidity cabinet test under relative humidity of 75 to 85 % and a temperature of 50 ° c . for 1000 hours . after these tests , filiform corrosion lengths from the cut portions were measured . the target plates were cross - cut and set in a salt spray tester for 1000 hours in accordance with the aforementioned jis - z - 2371 , for measurement of single - side maximum corrosion lengths from the cut surfaces . the target plates on which cutting was given were brought into a corrosive environment atmosphere for 60 cycles , and measurement was made similarly to the aforementioned salt spray test . each cycle was carried out as follows : salt spray ( jis - z - 2371 ) for 6 hours → drying ( at 50 ° c . for 3 hours )→ wetting ( at 50 ° c . under at least 95 % rh for 14 hours )→ room temperature drying ( at the room temperature for 1 hour ) table 1______________________________________ 1 2 3 4 5 6______________________________________composition na ( g / l ) 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0of treatment k ( g / l ) 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0solution mn ( g / l ) 0 . 6 0 . 6 0 . 6 0 . 6 0 . 6 0 . 6 ni ( g / l ) 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 zn ( g / l ) 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 0 . 8 f ( g / l ) 0 . 15 0 . 10 0 . 10 0 . 20 0 . 20 0 . 09 sif . sub . 6 ( g / l ) 1 . 00 1 . 00 1 . 00 1 . 00 1 . 00 1 . 00 no . sub . 3 ( g / l ) 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 no . sub . 2 ( g / l ) 0 . 06 0 . 06 0 . 06 0 . 06 0 . 06 0 . 06 fa ( po .) 0 . 6 0 . 8 0 . 4 0 . 9 0 . 5 1 . 0 temper - 40 40 40 40 40 60 ature (° c . ) weight of al 1 . 6 1 . 2 1 . 7 1 . 5 1 . 8 1 . 6coating fe 2 . 4 2 . 4 2 . 5 2 . 4 2 . 5 2 . 4 ( g / m . sup . 2 ) zn 2 . 8 2 . 8 2 . 9 2 . 8 2 . 9 2 . 8adhesion al 100 100 100 100 100 100 ( pieces ) fe 100 100 100 100 100 100 zn 100 100 100 100 100 100filiform al 1 . 0 2 . 5 1 . 0 1 . 5 1 . 5 1 . 5corrosion fe 1 . 6 1 . 5 2 . 0 1 . 6 2 . 2 1 . 4 ( mm ) zn 0 . 5 0 . 5 0 . 6 0 . 7 0 . 8 0 . 6salt spray al 0 . 5 1 . 0 0 . 4 0 . 8 0 . 7 0 . 5 ( mm ) fe 1 . 0 0 . 3 1 . 0 1 . 0 1 . 1 0 . 9 zn 1 . 5 1 . 2 1 . 3 1 . 8 1 . 9 1 . 5composite al 2 . 0 2 . 2 1 . 6 2 . 1 2 . 2 1 . 9corrosion fe 2 . 9 2 . 8 2 . 9 2 . 6 2 . 9 2 . 7 ( mm ) zn 2 . 3 2 . 2 2 . 2 2 . 4 2 . 4 2 . 2______________________________________ table 2______________________________________ 7 8 9 10 11 12______________________________________composition na ( g / l ) 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0of treatment k ( g / l ) 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0solution mn ( g / l ) 0 . 6 0 . 6 0 . 6 0 . 6 0 . 6 0 . 6 ni ( g / l ) 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 zn ( g / l ) 1 . 0 0 . 8 1 . 0 0 . 8 1 . 5 1 . 8 f ( g / l ) 0 . 06 0 . 06 0 . 12 0 . 12 0 . 18 0 . 38 sif . sub . 6 ( g / l ) 1 . 00 1 . 00 1 . 00 1 . 00 1 . 00 1 . 00 no . sub . 3 ( g / l ) 5 . 0 5 . 0 5 . 0 5 . 0 6 . 0 6 . 0 no . sub . 2 ( g / l ) 0 . 08 0 . 06 0 . 06 0 . 06 0 . 08 0 . 08 fa ( po .) 1 . 2 0 . 6 1 . 4 0 . 7 0 . 2 0 . 4 temper - 60 60 60 60 20 20 ature (° c . ) weight of al 1 . 3 1 . 7 1 . 3 1 . 8 1 . 3 1 . 2coating fe 2 . 3 2 . 4 2 . 2 2 . 4 2 . 5 2 . 3 ( g / m . sup . 2 ) zn 2 . 8 2 . 8 2 . 8 2 . 8 2 . 9 2 . 9adhesion al 100 100 100 100 100 100 ( pieces ) fe 100 100 100 100 100 100 zn 100 100 100 100 100 100filiform al 2 . 5 1 . 0 2 . 5 1 . 5 2 . 5 3 . 0corrosion fe 1 . 6 1 . 5 2 . 0 1 . 5 2 . 5 2 . 2 ( mm ) zn 0 . 5 0 . 5 0 . 6 0 . 6 0 . 8 0 . 8salt spray al 1 . 0 0 . 5 1 . 0 0 . 7 1 . 0 1 . 2 ( mm ) fe 0 . 9 0 . 8 1 . 0 0 . 8 1 . 1 1 . 0 zn 1 . 3 1 . 3 1 . 2 1 . 3 1 . 9 1 . 9composite al 2 . 0 1 . 9 2 . 1 2 . 0 2 . 5 2 . 2corrosion fe 2 . 6 2 . 6 2 . 7 2 . 6 3 . 0 2 . 9 ( mm ) zn 2 . 2 2 . 2 2 . 3 2 . 2 2 . 4 2 . 4______________________________________ table 3______________________________________ a b c d e f g______________________________________com - na ( g / l ) 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0position k ( g / l ) 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0 1 . 0treat mn ( g / l ) 0 . 6 0 . 6 0 . 6 0 . 6 0 . 5 0 . 6 0 . 6treat - ni ( g / l ) 1 . 0 1 . 0 1 . 0 1 . 0 0 . 3 1 . 0 1 . 0ment zn ( g / l ) 1 . 0 1 . 0 1 . 0 0 . 7 1 . 2 1 . 6 0 . 8solution f ( g / l ) 0 . 01 0 . 30 0 . 10 0 . 10 0 . 15 0 . 10 0 . 15 sif . sub . 6 1 . 00 1 . 00 1 . 00 1 . 00 1 . 00 1 . 00 1 . 00 ( g / l ) no . sub . 3 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 5 . 0 ( g / l ) no . sub . 2 0 . 06 0 . 06 0 . 06 0 . 06 0 . 06 0 . 06 0 . 08 ( g / l ) fa ( po .) 0 . 6 0 . 6 0 . 9 0 . 2 0 . 6 0 . 6 0 . 4 temper - 40 40 40 40 40 50 35 ature (° c . ) weight al 0 . 4 1 . 7 0 . 3 0 . 7 1 . 9 2 . 0 0 . 3of fe 2 . 4 2 . 4 2 . 4 1 . 9 2 . 4 2 . 6 1 . 9coating zn 2 . 8 2 . 7 2 . 8 2 . 2 2 . 8 3 . 2 2 . 3 ( g / m . sup . 2 ) adhesion al 100 100 100 100 50 80 90 ( pieces ) fe 100 100 100 90 50 50 50 zn 100 100 100 90 10 50 50filiform al 5 . 5 3 . 5 7 . 0 6 . 0 9 . 0 3 . 0 10 . 0corro - fe 1 . 7 1 . 8 1 . 6 3 . 0 3 . 0 1 . 9 4 . 0sion zn 0 . 6 0 . 8 0 . 5 0 . 9 0 . 9 0 . 7 0 . 6 ( mm ) salt al 3 . 1 1 . 2 3 . 5 3 . 2 3 . 5 2 . 0 3 . 5spray fe 1 . 0 1 . 2 1 . 0 3 . 0 2 . 5 2 . 5 3 . 9 ( mm ) zn 2 . 0 2 . 0 1 . 9 2 . 5 2 . 5 2 . 0 2 . 0com - al 4 . 2 4 . 2 4 . 2 4 . 2 4 . 3 3 . 5 4 . 5posite fe 2 . 8 2 . 9 2 . 7 4 . 5 3 . 8 3 . 1 3 . 9corro - zn 2 . 2 2 . 5 2 . 3 3 . 0 3 . 0 2 . 4 2 . 6sion ( mm ) ______________________________________ fig1 shows values of free f ion concentration and free acidity of examples 1 to 12 and comparative examples a to d . referring to fig1 □, ∘ and δ show values at 60 ° c ., 40 ° c . and 20 ° c . respectively . as clearly understood from fig1 comparative examples a to d are in positions separated from the region of 40 ° c . it is clearly understood from tables 1 and 2 that examples 1 to 12 according to the present invention have sufficient coating weights and obtain excellent results in the adhesion , filiform corrosion , salt spray and composite corrosion cycle tests in the al , fe and zn materials . on the other hand , comparative examples a to d are insufficient in filiform corrosion resistance of the al materials , and corrosion resistance in the salt spray test and the composite corrosion cycle test , despite the sufficient results in adhesion . comparative example e , having contents of mn and ni ions less than the inventive ranges , are inferior in adhesion and corrosion resistance . comparative example f , having a content of zn ions larger than the inventive range , is reduced in adhesion to the fe and zn materials , and inferior in corrosion resistance . comparative example g , having a small content of zn ions , is reduced in coating weight particularly with respect to the al material , and inferior in adhesion and corrosion resistance . although the present invention has been described and illustrated in detail , it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation , the spirit and scope of the present invention being limited only by the terms of the appended claims .