Novel modelling approach to optimisation of welding conditions and heat treatment schedules for age hardening Al alloys

Abstract

In the present paper the general purpose finite element code WELDSIM, equipped with a new natural aging model, is used to calculate the minimum heat affected zone (HAZ) strength level s min and the equivalent half width of the reduced strength zone Dy eq red of strength s min during single pass butt welding of Al-Mg-Si alloys. In particular, it is illustrated how the resulting strength loss depends on the interplay between the base metal chemistry and the initial temper condition on the one hand and the net arc power q 0 , the welding speed v, the plate thickness d and the effective heat transfer coefficient h between the Al plate and the steel backing on the other hand. Assuming one-dimensional heat flow and pseudosteady state, the former parameters can be combined in a single group variable q 0 /vd, which uniquely defines the HAZ thermal programme when welding is performed without the use of steel backing. Taking this as the main variable controlling the strength loss, the simulation results can be condensed into two-dimensional process diagrams, showing the variation in the design parameters s min and Dy eq red with q 0 /vd for different combinations of h and d. The output data from WELDSIM are, in turn, used as inputs to mechanical models to predict the resulting design stress under different loading conditions. It is concluded that significant weight reductions and cost savings can be achieved by minimising the strength loss after welding, provided that the design parameters s min and Dy eq red are calculated on the basis of the actual yield strength profile within the weld HAZ, as obtained from WELDSIM.

Perforation of welded aluminum components: Microstructure-based modeling and experimental validation

“…The simplified method described in Ref. [39] is adopted here to predict the effect of cluster formation and the associated yield strength increase during room temperature storing in regions where the peak temperature has been sufficiently high to cause partial or complete dissolution of the hardening b 00 particles during the welding, i.e. Zone 1 in Fig.…”

Exploring the hybrid metal extrusion and bonding process for butt welding of Al–Mg–Si alloys

“…In practice, a variety of factors may influence the properties of welded Al-Mg-Si components. The total width of the HAZ and subsequent strength loss in this region depend both on the base metal chemistry and the initial temper condition, as well as on the applied welding parameters which determine the HAZ T-t pattern [1,4]. Thus, following further optimization the HYB process needs to be benchmarked against GMAW and FSW under otherwise comparable conditions using exactly the same base material and plate thickness.…”

“…Although the Al-Mg-Si alloys are readily weldable, the excessive heat generation associated with the traditional welding processes makes them vulnerable to HAZ softening due to reversion of the hardening precipitates which form during artificial aging [3]. Despite that some strength recovery may be achieved by natural aging or by applying an appropriate post-weld heat treatment, the mechanical integrity of the welded component is always poorer than that of the base material [1,4]. Moreover, the material melting occurring during fusion welding makes the weld susceptible to pore formation, hot cracking, liquation cracking, and bonding defects causing additional degradation of the joint [1,2].…”

Qualification of the hybrid metal extrusion & bonding (HYB) process for welding of aluminium offshore structures

“…However, if the comparison instead is based on the yield strength data in Figure 5A, the corresponding strength reduction factors become 61% and 63%, respectively. The latter values are the ones being incorporated in current design codes for welded aluminium structures and used for calculating the maximum allowable design stress 21 . Because the observed difference between the FS and the HYB strength reduction factors is rather smaller, both welds are deemed to exhibit approximately the same load‐bearing capacity.…”