Precipitation processes in AlZn5Mg2CuX alloys

Abstract

AlZnMgCu alloys are important structural niaterials because of their high strengths and good stress corrosion resistance (SPEIDEL; ARCHAMBAULT, CHEVIER, BECK). The relationship between the properties and structure, as well as the formation of different phases in the ternary alloys are well known (UNGAR et al.; LOFFLER e t al.). However, the decornposition and trarisforniation processes in the quaternary AIZnMgCu alloys are not well known at present and there are several contradictions in the literature. Only a few systematical investigations have been made on the role of Cu i n the deconiFosition piocesses in the quaternary alloys (BRYANT; SOENO, CHIGASAKI).The aim of this work is to deterniine the effect of Cu addition on the precipitation processes i n the AlZn5Mg2 alloys. ExperimentalThe alloys were prepared of high purity alurniniuiu ancl alloying eleinents ancl cast in t t i~ induction furnace into iron mould. The composition of the alloys investigated can be seen in Table 1 . The samples were cut from sheets after cold rolling.Electrical resistance, tensile properties, inicrohardness measurements completed by clifferential scanning calorirnetry and X-ray sillall-angle scattering investigations have been conducted. The detttils of the experimental technics are published previously (UNQAR The processes investigated were the following : G1' zone formation at about room ternperature, Ostwald ripening above 60 "C and the fornmtion of transition phases between 130 .~i i d I80 "C. One part of kinetical iiieasureinents was carried out "in-situ" in a thermostat Lhe others a t roo111 teiiipertttirre or in liquid nitrogen after interrupting the heat treatrnent

The effect of Cu on mechanical and precipitation properties of Al–Zn–Mg alloys

“…This rate is strongly decreased by the addition of copper. The effect of Cu in the Al-Zn-Mg system was studied by several authors with controversial results concerning the question whether the addition of Cu accelerates or retards the formation of GP zones [18][19][20]. After the initial stage the strengthening introduced by the formation of GP zones takes place at a higher rate in the Cu-containing than in the ternary Al-Zn-Mg alloy.…”