Effect Of Mg On The Portevin-Le Chatelier Characteristics Of Al-Mg Aluminum Alloy Sheets At Room Temperature

The Al-Mg aluminum alloy,which has excellent weldability,high corrosion resistance and good strength,is widely used in shipbuilding,automotive,aerospace and industrial construction.However,the phenomenon of the Portevin-Le Chatelier(PLC)effect is easy to appear in the plastic process,especially in the tensile deformation process of Al-Mg aluminum alloy.The PLC effect will occur repeatedly during the whole plastic deformation process.On the one hand,the PLC effect makes the surfaces of the products rough and reduces the surface quality;on the other hand,the PLC effect also reduces the ductility and affects the resisitance to fatigue of the material,greatly reducing the materials formability.Factors that influence the results of the PLC effect include external parameters and internal parameters.The external factors which have attracted much attention of researchers mainly include strain rate and deformation temperature,and internal factors mainly include alloy composition,grain size and solute concentration et al.The configuration of precipitate particles has an important influence on the dynamic strain aging process of Al-Mg alloy,which can affect the occurrence and development of the PLC effect.However,there are few studies about the effect of the precipitate particles configuration on the PLC effect of Al-Mg alloy.In this study,the annealing temperature(200??550?)of 5083 aluminum alloy sheets was controlled to change the size,number and distribution of ? phase,in order to study the effect law of the ? phase particles configuration on the PLC effect of 5083 alloy sheets tensiled at room temperature.Then on the base of these,the effect of Mg content(2.86%,4.23%,6.44%,6.51%and 9.41%)on the PLC effect of Al-Mg alloy sheet tensiled at room temperature was further studied.Following is the main studying conclusions:1.The annealing temperature increased from 200? to 550? has no obvious influence on the size,number and distribution of excess crystalline phase.The grians of cold rolled 5083 aluminum alloy sheets annealed at 200? still remains fibrous and there are a number of dislocations in the matrix.Recrystallization occurs in the cold rolled 5083 aluminum alloy sheets as annealed at 250?.2.Complete recrystallization occurs in the hot rolled Al-(2.86?9.41)Mg sheets as annealed and quenched at 450? and their grians both tend to be nearly equiaxed in shape.The Mg content increased from 2.86%to 9.41%have no obvious influence on recrystallization grain size.A large number of second-phase particles are observed in the alloys matrices and these particles were distributed as broken chains along the rolling direction.The number of second phase particles in the annealed alloy sheets increases and the number of second phase particles in quenched alloy sheets remain unchanged with the increase of Mg content.The number of ? phase in the annealed sheets is much more than that of the quenched sheets for the same Mg content and the number of ? phase in the annealed alloy sheets increases with the increase of Mg content.3.When tensiled at 1×10-5s-1,the 5083 aluminum alloy sheets annealed at 250? 300?and 350? don't occur PLC effect while the 5083 aluminum sheets all occur obvious PLC effect annealed at temperature more than 350?.When tensiled at the strain rates more than 1×10-4s-1 at room temperature,the PLC effect is observed in all annealed 5083 aluminum alloy sheets.The stress drop of annealed 5083 aluminum alloy sheets first increase and then decrease with the annealing temperature increased from 200? to 550? and the stress drop arrives at the maximum value at 400?.4.The critical strain of all annealed 5083 aluminum alloy sheets tensiled at room temperature all first decreases and then increases with the strain rate increased from 1×10-5s-1 to 1×10-2s-1 and the critical strain arrives at minimum value at 1×10-3s-1.The stress drop,waiting time and falling time all decreases with the increase of strain rates.5.The PLC effect is observed in all annealed and quenched Al-(2.86?9.41)Mg alloy sheets tensiled at room temperature and 1×10-3s-1.The critical strain of all annealed and quenched Al-Mg alloy sheets tensiled at room temperature all first decreases and then increases with the Mg content increased from 2.86%to 9.41%.And the critical strain of Al-4.23Mg is the lowest.6.At the same strain,the stress drop and waiting time of annealed and quenched Al-(2.86?9.41)Mg alloy sheets tensiled at room temperature increases with the increase of Mg content while the falling time changes little.For the same Mg content of Al-(2.86?9.41)Mg alloy sheets,the stress drop of annealed alloy sheets is higher than that of quenched alloy sheets and their waiting time and falling time is almost the same.7.When the Mg content is less than 4.23%,the critical strain of annealed Al-Mg alloy sheets tensiled at room temperature is higher than that of quenched Al-Mg alloy sheets and when the Mg content is more than 4.23%,the critical strain of annealed Al-Mg alloy sheets tensiled at room temperature is lower than that of quenched Al-Mg alloy sheets.