fig1 shows zones ( 1 ) of random shape and width distributed in a random manner , but which have in each case a width between 10 and 100 μm and a percentage surface fraction of between 5 and 60 % of the area of the wear - resistant surface of the casting . fig2 shows zones regularly arranged in accordance with a square mesh network constituted by bands ( 2 ) having a width of 40 μm and spaced from one another by 360 μm . fig3 shows punctiform zones ( 3 ) with a size of 50 μm and spaced from one another by 100 μm . fig4 is a microphotograph , with a magnification of 100 , of zones distributed in accordance with bands with a width of 40 μm , spaced by 200 μm and intersecting ar right angles , the zones being obtained on an aluminium alloy casting of type a - s17u4g ( 17 % silicon , 4 % copper , & lt ; 1 % magnesium and the remainder aluminium ). fig5 and 7 will be referred to during the description of the following example . castings of a - s5u3 ( i . e . containing by weight 5 % silicon , 3 % copper and the remainder aluminium and impurities ) and a - s17u4g ( 17 % si , 4 % cu , & lt ; 1 % mg ) all produced in the same way , were subdivided into two batches 1 and 2 , both batches having both alloy types . batch 1 underwent a laser treatment to obtain zones in accordance with the prior art and batch 2 underwent another laser treatment to obtain zones according to the invention . the conditions of these treatments are as follows : ______________________________________ batch 1 batch 2______________________________________laser beam co . sub . 2 arpower ( watts ) . sup . 2500 . sup . 18beam width ( μm ) . sup . 1000 . sup . 20power density ( watts / cm . sup . 2 ) 2 . 5 × 10 . sup . 6 7 × 10 . sup . 6treatment duration ( sec ) 6 / 100 1 / 40treated zone width ( μm ) ≃ 3000 ≃ 40treated zone depth ( μm ) ≃ 2600 ≃ 20______________________________________ from the relief of fig5 showing in section and a magnification of 25 a batch 1 casting having a zone ( 4 ), there is seen a raised macroscopic relief extending over the entire width of the zone and whose amplitude reaches 100 μm , so that remachining of the casting is necessary . the casting of batch 2 ( fig6 ) shows in section , and with a magnification of 1000 , a zone ( 5 ) having no macroscopic relief but only the microroughness is slightly affected . thus the batch 2 castings require no remachining . in fig5 and 6 , it is also possible to see a radical structural change at the zones , permitting a precise location of the zones and the measurement of their dimensions . on both batches , a vickers hardness exceeding 200 was measured in the zones , whereas it was 80 between the zones . therefore , the castings according to the invention , and which consequently have zones of limited width and depth , have a degree of deformation of the surface profile making it unnecessary to machine them . other castings of the same type were previously coated with an iron film by electrolysis in a quantity such that , after melting , it was possible to produce on the surface a 15 % iron alloy . these castings were also distributed into two batches , which underwent the same treatments as those described hereinbefore , with the exception of the arrangement of the treated zones . thus , the surfaces of the castings of batch 1 ( prior art ) were treated along unidirectional parallel bands , which overlapped ( batch 1a ), or which did not overlap ( batch 1b ), with the distance between the bands being 2000 μm , whereas the surfaces of the batch 2 castings were treated along a network of parallel bands intersecting at right angles and spaced from one another by 200 μm . micrographic examination of the surfaces revealed that in certain cases the treated zones of batches 1a and 1b suffered from cracking ( 6 ) ( fig7 ), whereas those of batch 2 were uncracked . in another series of tests , the iron was replaced by galvanic deposition of nickel , so as to produce on the surface after melting a 10 % nickel alloy , and the castings of both batches underwent friction -- wear measurements using the cameron - plint tribometer . this tribometer is constituted by a ferrochromium segment , which bears on the surface to be checked and which performs an alternating movement , so as to approximately simulate the friction occurring between the segments inserted in the piston and jacket of an internal combustion engine . in these tests , the bearing load was 100 n , the casting temperature 100 ° c ., the frequency of the movement 12 hz and the test duration 30 minutes . the surface was previously lubricated with a neutral 150 oil . the castings of batch 1 were subject to rapid deterioration ( detachment of large debris & gt ; 1 μm from the treated surface ) and this also applied to the ferrochromium segment . however , in the case of the castings in batch 2 , there was no visible deterioration or measurable weight loss . the present invention can be used in the production of castings subject to friction , such as e . g . mechanical parts ( jackets of engines and pistons , valve seats , brake disks and drums , notched driving pulleys , die plates , gears , dies , drive shaft bearings , ball bearings , etc .) and electric contact parts where there is a combination of friction and the passage of electric current ( connectors , sliding contacts , electric motor commutators , etc .). obviously , numerous ( additional ) modifications and variations of the presnt invention are possible in light of the above teachings . it is therefore to be understood that within the scope of the appended claims , the invention may be practiced otherwise than as specifically described herein .