Effect of thixoextrusion parameters on mechanical properties of 7003 Aluminum wrought alloy

The processing of high strength Al wrought alloys does lead either to restrictions for geometrical complexity or to high production costs due to low productivity and multiple-step processes. Thixoextrusion process to overcome these difficulties has been under investigation. In the present study, the effect of thixoextrusion parameters was investigated on mechanical properties of 7003 Al wrought alloy. The maximum extrusion pressure of the thixoextrusion process is three times lower than that of the hot extrusion process. The elongated grains which have the axisymmetry with extrusion direction are generally observed during hot extrusion process, while the microstructures of the thixoextruded are isotropic. The tensile and yield strengthes of the thixoextruded bar are lower than those of the hot extruded bar, while the elongation value of the thixoextruded bar is higher than that of the hot extruded bar.

Effects of cathodic polarization on SCC behavior of AA7003 under various aging treatments

In this paper,the effect of cathodic polarization on corrosion behavior of AA7003 under three kinds of aging treatments(including peak aging(PA),double peak aging(DPA)and regression re-aging(RRA))was studied in 3.5 wt%sodium chloride solution through slow strain rate testing(SSRT)and electrochemical testing.X-ray diffraction(XRD)and scanning electron microscopy(SEM)methods were also applied to investigating corrosion behavior and fracture morphology.The results showed that under open circuit,stress corrosion cracking(SCC)of AA7003 might by classified as anodic dissolution.In this case,the extent of SCC susceptibility(ISCC)of AA7003 alloy with different aging treatments was as follows:ISCC(PA)>ISCC(DPA)>ISCC(RRA).On the other hand,stress corrosion cracking(SCC)of AA7003 under cathodic polarization might be classified as hydrogen embrittlement(HE)which had been proved in this paper by presence of AlH3 diffraction peak in XRD patterns.In this case,for AA7003 with any of the three aging treatments,hydrogen embrittlement susceptibility(IHE)increases with negatively shifting of cathodic polarization.

Localized Corrosion and Stress Corrosion Cracking Behavior of AA7003 in a 3.5 wt% NaCl Aqueous Solution

The microstructure,localized corrosion (LC) and stress corrosion cracking (SCC) behavior of 7003 aluminum alloy (AA7003) under various aging treatments (peak aging (PA),double peak aging (DPA),regression and re-aging (RRA)) were investigated by means of transmission electron microscope (TEM),scanning electron microscopy (SEM),electrochemical impendence spectroscopy (EIS) and slow strain rate tensile test.The results of TEM showed a discontinuous distribution of grain boundary precipitates of AA7003 under DPA and RRA treatments,which is beneficial for increasing the resistance of LC and SCC.Meanwhile,LC was found initiating firstly on intermetallics which caused the dissolution of surrounding matrix,then pitting holes were formed and developed into matrix.In addition,the SCC process of AA7003 could be divided into two stages,i e,initial pre-cracking and breeding cracking.The EIS analysis,cross-section morphologies and fracture surfaces of specimens indicated that DPA and RRA treatments significantly decreased the crack growth rate during breeding cracking stage,especially for RRA treatment.