ER70S-6 is classified within A5.18.
Within A5.18 I find the following, CO2 is the standard shielding gas required by A5.18 for tensile tests performed by the filler metal manufacturer's in order for them to classify their products to E70S-6. However, see note c below which is tagged to the CO2 in the table.
"c. CO2 = carbon dioxide shielding gas (AWS A5.32 Class SG-C). The use of CO2 for classification purposes shall not be construed to preclude the use of Ar/CO2 (AWS A5.32 Class SG-AC-Y) or Ar/O2 (AWS A5.32 Class SG-AO-X) shielding gas mixtures. A filler metal tested with gas blends, such as Ar/O2, or Ar/CO2, may result in weld metal having higher strength and lower elongation. Testing with 100% argon shielding (AWS A5.32 Class SG-A) is required when classification testing is based on GTAW only (see A4.2 in Annex A)."
A5.18 also states the following in its annex:
"A7.4 ER70S-6 [ER48S-6]. Electrodes and rods of the ER70S-6 [ER48S-6] classification are intended for both single- and multiple-pass welding. They are especially suited for sheet metal applications, where smooth weld beads are desired, and structural and plate steels that
have moderate amounts of rust or mill scale. These electrodes permit the use of higher current ranges with either CO2 (AWS A5.32 Class SG-C) shielding gas or with mixtures of argon and oxygen (AWS A5.32 Class SGAO-X) or argon and carbon dioxide (AWS A5.32 Class
SG-AC-Y). However, these electrodes do require a higher level of oxidation than the previously described electrodes when using either binary or ternary argon shielding gas mixtures per the AWS A5.32 specification. Typical base metal specifications are often the same as those for the ER70S-2 [ER48S-2] classification."
The D1.1 code also requires all shielding gases to conform to A5.32 which I expect Blueshield 7 does but you need to verify.