Quench sensitivity and microstructure character of high strength AA7050

The effect of quenching rate on the electrical conductivity and microstructure of thick plates of incumbent AA7050 was investigated by employing Jominy end quench test. The electrical conductivity measurement and microstructural observation were conducted at different distances from the quenched end. The results indicate that the average cooling rates decrease with increasing the distance from the quenched end of the bar in the quench sensitive temperature range. However, the electrical conductivity increases with the increase of distance from the quenched end. The surface parts of the plate were fully recrystallized, while partial recrystallization took place at the quarter and center parts of the plate. The quench induced grain boundary precipitates became remarkably coarser and discontinuously distributed with increasing distance from the quenched end of the bar. Plenty of heterogeneous precipitates were observed to nucleate on A13Zr dispersoids when the distance from the quenched end was greater than 38mm.

Quench sensitivity of novel Al-Zn-Mg-Cu alloys containing different Cu contents

The effect of copper content on quench sensitivity in novel Al-Zn-Mg-Cu alloys containing high zinc content was investigated by Jominy end quench test.Electrical conductivity and hardness test,temperature collecting,and transmission electron microscopy(TEM)technique were adopted for the properties and microstructure characterization of three alloys with different copper contents.The results indicate that the electrical conductivity of all three alloys increases with the increase of distance from the quenched end,while the hardness shows an opposite trend.If the dropping of 10%hardness is defined as the critical evaluation standard of quenching,the depth of quenched layer of AlloysⅠ,Ⅱ,andⅢare 70,55,and 40 mm,respectively.The precipitation behavior on grain boundaries of three alloys is similar except for a little difference in size,while the size of precipitates in grains of AlloyⅢwith higher copper content is larger than those of the other two alloys at the same location.Considering all results,the stability of the supersaturated solid solution of AlloyⅢis lower than those of the other two alloys,meaning that AlloyⅢshows the highest quench sensitivity.Higher copper content leads to higher quench sensitivity in novel Al-Zn-Mg-Cu alloys with the same content of magnesium,zinc,and other trace elements.