Differential Scanning Calorimetry Fingerprints of Various Heat-Treatment Tempers of Different Aluminum Alloys

Heat-treatable cast and wrought aluminum alloys are widely used for structural applications in the automobile and aerospace industries. To assess and diagnose the production and quality problems related to industrial heat treatments, differential scanning calorimetry (DSC) was used as a tool in the present work to determine the thermal histories of samples that had undergone different tempers of three commonly used aluminum alloys, namely a high-pressure die-cast AlSi10Mg0.3Mn alloy, permanent-mold cast Al-Si-Cu 319 alloy, and extruded Al-Mg-Si AA6082 alloy. Various peaks detected in the DSC curves were analyzed and characterized to identify the precipitation/dissolution reactions of metastable phases, aiming to establish a “fingerprint” of each temper of the three experimental alloys. Results showed that both the number and size of exothermic peaks varied with the temper owing to distinct precipitation behaviors, providing an effective means of fingerprinting the various tempers. Meanwhile, electrical conductivity and microhardness data provided the supplementary support for the fingerprinting. The thermal histories of three experimentally heat-treated alloys were well traced and distinguished by the combination of DSC characteristics and electrical conductivity and microhardness results, promoting the DSC application in the quality control and verification of industrial heat treatments. In addition, the microstructures after the various tempers were observed to confirm the evolution of the precipitation reactions revealed in the DSC curves.

Warm Forming and Paint Bake Response of AW-7xxx Sheet in Various Tempers

In this paper, we have investigated AW-7921 in various tempers - specifically under aged T4P1-and T4P2-tempers, naturally aged T4 and peak-aged T6-tempers - for their warm formability at 230°C and paint baking response through one step and five step paint baking treatments. It was found that warm formability depends on dynamic recovery and dissolution of precipitates. However, the response to paint baking was dependent on the stability of the precipitates against coarsening. Of the tempers investigated the T4-temper exhibited the best combination of formability and paint baking response. This study also indicated that we can achieve much better performance in the warm forming processing chain by optimization of the temper and paint baking heat treatment procedure.