Research Of The Microstructure And Corrosion Behavior Of TA2 And TC4 By FSP

Titanium alloys are widely used in aerospace,marine equipment engineering and other fields because of their high specific strength,high hardness and excellent corrosion resistance.As one kind of marine engineering materials,some Titanium alloys are named as marine metal because of their special properties.In this paper,friction stir processing technology(FSP)was used to prepare fine-grained TA2 commercial pure titanium and TC4 titanium alloy.Their microstructure and corrosion behavior in the simulated marine environment have been investigated by advanced testing methods.The main results are as follows:(1)When the suitable processing parameters were used,the grain sizes of CP TA2 and TC4 alloy were obviously refined by FSP.As far as TA2 is concerned,the grain size was the smallest at 0.5 mm from the machined surface,which was refined from 29.35 ?m to 1.83 ?m.As far as TC4 alloy is concerned,the grain size of the sample increased with the increase of the rotating speed of the stirring head at the same processing speed.Under the same rotating speed of the stirring head,the grain size increased with the increase of the processing speed.In this study,the surface formability of the sample processed at the rotating speed of 200 r/min and 25 mm/min was the best.The surface grain size was the smallest,which was refined from the original 4.87?m to 0.4?m.(2)The texture of TA2 commercial pure titanium and TC4 titanium alloy has changed obviously after friction stir processing.The texture of TA2 commercial pure titanium has changed from original 112 0 //RD texture to more 101 0 //ND texture,and the density of pole increases after processing.The c axis of TC4 titanium alloy grains has changed from original mainly in the direction of TD to the direction of RD after processing.The polar density decreased with the increase of rotational speed,but increased with increasing of processing speed.(3)Grain refinement contributes to the formation of passivation film.After friction stir processing,the passivation film of CP TA2 was the thickest at 1.0 mm from the machined surface,while that of the original sample was the thinnest.The passivation film of TC4 titanium alloy was the thickest after processing at a speed of 200 r/min and a processing speed of 50 mm/min.(4)After friction stir processing,the corrosion behavior of TA2 and TC4 was both improved.As far as TA2 is concerned,,the corrosion resistance of the sample with grain size of 2.01?m at 1.0 mm from the machined surface was the best,which was 39% higher than that of the original sample with grain size of 29.35?m on average;As far as TC4 alloy is concerned,the corrosion resistance with 1.1?m after 200r/min-50mm/min processing was the best,which was 42% higher than that of the original sample with grain size of 4.87 um on average.