EMP2.1 Batch Uniformity Proved by Means of Electrical Conductivity Measurement Influenced by Solution Heat Treatment Only?

Tuesday, June 19, 2012: 8:30 AM
219AB (Charlotte Convention Center)
Dr. Christoph Henkel , AMAG rolling, Ranshofen, Austria
Reinhardt Rachlitz , AMAG rolling, Ranshofen, Austria
Holm Böttcher , AMAG Casting, Ranshofen, Austria
The batch uniformity of aircraft plates has to be proven by means of electrical conductivity measurements. The absolute value is influenced by the solution heat treatment as well as the natural and / or artificial aging. The difference value is normally controlled by the quench conditions after solution heat treatment. Sporadically, in 7075 plates in temper T7351 conductivity differences of up to 1.5 MS/m occurred, i.e. above the tolerance limit, so that the plates had to be scraped.

The mechanical properties are not affected by these conductivity differences. At the first root cause analysis solution heat treatment variations could be excluded too. In the following the whole process chain was investigated systematically, beginning with the chemical composition of the ingot up to the artificial aging of the final plates. 

The investigations proved that the conductivity differences were caused by Cr-precipitations, which arise in an early stage of the production and cannot be solved afterwards.