Effects Of Heat Treatment On The Microstructures And Mechanical Properties Of The Cast Modified Al-Cu Alloy

The demanding of light-weight in automobile and aviation industry,which promote the development of high strength and toughness aluminum alloys.According to the as-cast Al-Cu alloy being the common structure materials in aerospace field,raising the material intensity imply to lighten structure mass,increase a payload.The intensity of the as-cast Al-Cu alloy is maximum in the middle of aluminium alloy,therefore our country spread omnidirectional research,to look forward to being much better application.The research of handicraft and theory of heat treatment on ZL205 modified by 1.5 wt.% Pr_xO_y appears very weak comparatively.The kind process which is obtain are mainly from the cognition of the technics of ZL205.But since the alloy joint the innocant Pr_xO_y during the course of casting,the craft of heat trentment may exist certain differences.Besides,since unitary heat treatment method become difficult in improving those function further,the electric field treatment as effective obdurability means are regarded highly.The home and abroad metallurgy and the material science worker have extremely aroused large interest on the technology of electric field changing nature in recent years.At present,large amount of research indicate that electric field heat treatment can accelerate homogenization and boost second-phase precipitation,which have become a sort of method controlling the structure and capability of material.The technology has non-polluting,simple, effective,etc.,so much attention has been foetus on.In view of the above-mentioned,One aspect has the fine mechanics function and the broad prospect in the automobile and aviation;Another aspect is that heat treatment can meliorate organization structure and improve mechanical behaviour.The paper takes as-cast Al-Cu alloy as study object,and research the craft of the common heat treatment and disclosure the re ated rule.Meanwhile there are a few researches concerned with the effect of electric field on heat treatment of as-cast A1-Cu alloy.All above has important significant of theory and practice to make high tensile strength and ductility aluminum alloys.The major research efforts of the present study are as follow:1) The higher solution heat-treatment(T4) temperature is in favor for dissolving ofθphase located in as-cast Al-5wt.%Cu alloy modified by 1.5wt.%Pr_xO_y alloy.But the too high solution temperature will make grain coarse and growing up and lead to the low mechanical properties.Under given temperature,the longer solution time will make grains coarse and growing up.The higher aging heat treatment(T6) temperature is favor of precipitation ofθ-phase fromα-Al-based grains.If aging temperature is too higher,the degree of dispersion of precipitation will be reduced,which will not be favor of mechanical properties of aluminium alloys.Under given temperature,the longer aging time will make precipitation phase coarse,getting together and globalizing,which will seriously reduce the mechanical properties of aluminum alloy.The reasons are as follows:when aging goes on to a certain degree,the dissolution and precipitation of solute will reach a balance.This balance is a dynamic balance,that is,solute is still in the process of solutionizing and precipitating.In this process,for reducing free energy,the precipitation phase will redistribute,accumulate and grow up to a advantageous orientation,which make precipitation phase globalizing and growing up at the late stage of aging and the alloy is in the over-aged state.2) The temperature 490℃,505℃,520℃of solution treatment imposed DC current,all restrain the dissolution of eutectic phase.But with the increasing of DC current,the effect of solution treatment become more and more nice.When the temperature reaches 535℃, exerting DC currents can promote the second phase dissolve in a short time.Energy spectrum analysis shows that the solution temperature of 535℃for 2 hours imposed by DC current,Cu atoms distributed more evenly.But the imposition of the electric current generated for the dynamic migration process,the solution treatment for the long time will lead to dissolved Cu atoms.In this paper,the best solution treatment(T4) process for as-cast Al-Cu alloy modified by 1.5wt.%Pr_xO_y as follows:solution treatment temperature can choose 535℃and combine a short period of time processed by DC currents with common solution treatment,which can shorten timeof solution treatment and improve efficiency in that conditions.3) The ZL205 alloy which is modified by 1.5wt.%Pr_xO_y,after imposed DC current,the two aging curves all have clear peaks and the softening stage.However,after imposing the direct current,the macro-hardness is lower than those common aging treatment,meanwhile that has decline moderately comparing general aging treatment.The second phaseθ′were hindered when the direct current was plused in aging treatment.We think the action of the electric current not only make the phaseθ′gathered, but also restrained solid-state phase changes.The phenomenon may relate with conductivity between the two-phase.Thefracture morphology also shown the uneven pattern after impositing direct current,which be cleavage and uneven dimples.In such conditions,the way of pulsing low-density DC current in aging treatment is not as the appropriate choice to optimize or meliorate the heat treatment system.