TIG Drawn Arc Stud Welding Process for 7A52 Aluminum Alloy

Literature Overview

This 2015 study published in Welding by Zhang De'ku, Yang Weilin, Wang Kehong, and Zhou Qi from the School of Materials Science and Engineering, Nanjing University of Science and Technology, investigates the application of TIG-drawn arc stud welding to 7A52 aluminum alloy. Funded by the Jiangsu Provincial Natural Science Foundation (BK20131261), this research explores a hybrid welding process that combines the arc stability of TIG welding with the productivity advantages of stud welding.

Core Technical Analysis

7A52 aluminum alloy (Al-Zn-Mg-Cu system, approximately 5.6% Zn, 2.5% Mg, 1.2% Cu) is a high-strength aerospace aluminum alloy used in structural components requiring excellent fatigue resistance and corrosion resistance. The alloy achieves tensile strength of 570–620 MPa in the T7 temper condition, but welding presents significant challenges due to its high hot cracking susceptibility and sensitivity to thermal cycling.

Process Principle

The TIG-drawn arc stud welding process operates on the following principle:

A TIG arc is established between a tungsten electrode and the workpiece
The stud (weld rod) is fed into the arc zone
The arc is "drawn" along the stud as it melts progressively
The molten stud material transfers to the weld pool in a controlled manner
The arc moves along the joint in a continuous or pulsating fashion

This differs from conventional stud welding in that the arc is not struck directly on the stud but is drawn from a separate electrode, providing better control over the heat input and arc stability.

Process Parameters

Parameter	Range	Optimal Value
Arc Current (A)	80–150	110–130
Arc Voltage (V)	12–16	14–15
Stud Feed Rate (mm/s)	5–15	8–12
Travel Speed (mm/min)	100–300	180–220
Shielding Gas Flow (L/min)	12–18	15
Stud Diameter (mm)	2.0–3.2	2.4–2.8
Electrode Stickout (mm)	8–15	10–12

Microstructural Characteristics

The weld metal in 7A52 aluminum alloy TIG-drawn arc stud welds exhibits:

Columnar dendrite structure with equiaxed grains near the fusion boundary
Precipitation of η-phase (MgZn2) and T-phase (MgZn2Al3) in the weld metal
Limited formation of coarse precipitates due to moderate heat input
HAZ with partial dissolution of strengthening precipitates

Defect Analysis and Countermeasures

The primary challenges in welding 7A52 aluminum alloy include:

Defect	Mechanism	Prevention Strategy
Hot cracking	Low melting point Al-Zn eutectic at grain boundaries	Add Cu to filler metal, control cooling rate
Undercut	Excessive arc energy at joint edges	Reduce current at edges, use proper joint preparation
Porosity	Hydrogen absorption from moisture	Strict surface cleaning, dry shielding gas
Excessive dilution	High heat input from stud	Reduce stud diameter, increase travel speed
Arc instability	Poor arc transfer to stud	Optimize stickout, maintain consistent feed rate

Engineering Practice Integration

The TIG-drawn arc stud welding process offers several advantages for aerospace manufacturing:

Higher deposition rates than conventional TIG welding (1.5–2.0x improvement)
Better arc stability than plasma arc welding for thin sections
Reduced tungsten contamination compared to conventional TIG
Suitable for automated welding with consistent quality
Applicable to complex geometries with limited access

For aerospace applications, this process is particularly suitable for:

Repair welding of 7A52 structural components
Welding of thin-section components (3–8 mm)
Production welding of repetitive joints
Fillet welds and T-joints where penetration control is critical

Study Insights and Reflections

The TIG-drawn arc stud welding process represents an innovative approach to combining the precision of arc welding with the productivity of consumable electrode processes. The key innovation lies in the separation of the arc-striking function (performed by the tungsten electrode) from the metal-deposition function (performed by the stud), which provides superior control over the welding process.

The process is particularly valuable for high-strength aluminum alloys like 7A52 where conventional welding methods often struggle to balance productivity with weld quality. The moderate heat input and stable arc characteristics make it well-suited for alloys with high hot cracking susceptibility, as the controlled thermal cycle reduces the time spent in the critical temperature range for cracking.